I never ST:E, BG or Seinfeld. After reflection, I would say that HIMYM was a good finale, the problem (as you suggest with Angel) was context. It would have been an awesome end to the show after season five or even six. After the excessive set up in the last few seasons though, they completely misplayed the build up to the ending or else were too locked into the finale they had planned, rather than adapting to accommodate what they had spent two or three years building up. They sold the head fake too hard, or else padded the last few seasons with too much minutiae or too many distractions.

Firefly, while it ended badly for non-show reasons, had a decent wrap up last DVD episode with "Objects in Space" and "Serenity" was a good enough finale.

While I would conceded your point with Angelo's last season, regarding how the ending seemed rushed and sprung on them out of left field, I think it did the job it was supposed to do, and was a very well-done episode. The last season was not perfect (but what 22 episode season ever is? ), but was a very thematically tight, and hit the magic/real-problem metaphors way better than anything Buffy had since season three.

I didn't see DS9, Oz or TB. I thought the Sopranos was excellent, and I don't get the disappointment, though I was never all that enthusiastic about the show in general. I thought it was okay, and a little pretentious. So I'm pretty out of touch with the rest of the audience. Friends, IMO, didn't really have much of an ending, so much as winding down. I wasn't invested in Ross & Rachel, so I didn't really care about the plot of the last episode. It was just wrapping up the ongoing arcs fairly predictably and done. I loved the Lost finale. It was obvious from the two big flashback episodes earlier in the season, (Ab Aeterno & Across the Sea, I think) which were extremely short on the promised answers, that we were not going to be getting any. Instead, it was about rooting for the characters rather than getting invested in the mysteries of the Island or the Sideline. And the latter device was an excellent mechanism to have our cake and eat it too. The lives and deaths we had watched meant something, but we also got reunions and fulfillment of the characters.

I have not yet seen Spartacus, I only saw a couple episodes of STNG, but the finale was among them, and I saw almost nothing of Voyager. I thought the TNG finale was good, but my attitude toward both Data and Picard, based on all the films was 'less is more' and the finale did nothing to dispel that notion. I never found the "grappling with what it means to be human" crap to be interesting, having a personally dogmatic perspective on that issue (just like questions of death, or the meaning of life), which from what I have seen, would render much of Data's characterization tiresome. And of course, I suspect he's a massive source of plot holes and inconsistencies. I also get the impression that Picard was intended to be a more realistic naval captain, i.e. one who stayed aboard the ship, with Riker doing the away missions, but that seems to have faded over time as he took on a more Kirk-like role, at which he could only be a pale imitation, IMO.

As for BtVS, I don't see how you have ranked it as you given your rationale for ranking Angel as you did. If "Not Fade Away" was handicapped by the season's flaws, how much more so must "Chosen be so considered? After about episode 7, that season began the horribly uneven "First Evil" storyline that dragged on way too long, assassinated most of the characters, featured too much Andrew, and was obviously playing manipulative games, trying to have its cake and eat it as Lost did with the Sideline, but lacking a clever mechanism. They tried to make the stakes real, by killing off a bunch of recently introduced cannon fodder. They tried to give "serious consequences" to a core cast member but only poked out one of Xander's eyes, which doesn't really adversely affect his quality of life or ruin the planned happy ending. They blatantly killed off Anya because she was the biggest character outside the core group, after spending the majority of the season demonstrating how they had not thought of any arc for her following her long-belated spotlight episode earlier in the year. They invented the ubervampires in the Turok-Han, only to either oversell their power when introduced, or render them so embarrassingly impotent that relatively untrained skinny teenaged girls are dispatching them with ease in great numbers in the final battle. The plan that was supposedly the capstone of Buffy's career basically amounted to that famous cartoon of two scientists looking at a blackboard full of equations, with one telling the other "You need to be more specific here..." referencing a point in the middle of equation saying "then a miracle happens". In fact, the BtVS finale only enhanced the significance of Angel, by both recalling a villain who had first come on the scene to try eliminating Angel, while more or less ignoring the Slayer, and then being defeated by a throwaway trinket provided by Angel's arch-nemesis. Her plan was:
Step 1. march a bunch of new Slayers into the Hellmouth
Step 2. ???????
Step 3. Evil destroyed, girl power triumphs! Hooray!

Where Angel's finale was a realistic look at the corruption of power and how choice is far more important than power, particularly the importance of making the right choice, Buffy's finale has a simple-minded and adolescent theme of "power, yay! Consequences? What's that?". Angel's final words were affirming that making the right choices mattered, regardless of how much power you had or what the outcome. Buffy's were reveling in having power and the ability to make whatever choice you want. It's fitting, I suppose, because at its heart, BtVS was inspired by, and a playing out of, wish fulfillment. The monsters represented the trials and ordeals of adolescence, and Buffy would slay those metaphorical demons in a literal sense, because she happened to be more powerful. An issue that was raised near the end of the last season, when Anya pointed out that her power was unearned and her leadership unproven, and immediately forgotten, serving only to exacerbate her nadir without actually addressing that issue. In the end, Buffy gets what teenage Buffy always wanted - freedom from responsibility, from obligation, from duty. If her struggle was a metaphor for adolescence, she did not end the struggle by growing up, but by reverting to childhood. Angel, on the other hand, was about finding your path, and the pursuit of redemption. In the end, he found that there was no easy triumph, no last battle. Adulthood is getting up each day to do it all over again. There is no graduation or ultimate vindication of your efforts, no long summer breaks. Instead you go out and struggle constantly with the goal of getting a little bit ahead to stave off your ultimate defeat. No Angel season ended on an upbeat note, like seasons 1, 3, 4, 6 & 7 and even, from a certain perspective, 5, of Buffy. It's worth noting that the grimmest, darkest season finale was season 2, which was heavily Angel-centric, and as much about him as her.

Both finales captured the theme of the show at its heyday, and expressed it in the finale scene, but Angel's finale actually fulfilled it's central premise.

As for other finales I have seen:
Dexter - Bad. It had strayed too far afield from the realization of what Dexter was and made his superficial excuses and cover story into the reality of his character because it was more palatable, and then tried to turn serious and moralizing with a bunch of random strokes of bad luck that were supposed to represent his chickens coming home to roost. They abandoned that road with the cheat ending to season 2, that allowed them to hit the reset button without making him commit to a course of action that would have either irrevocably defined his character or permanently changed his life. It let the show go on in the successful format it had established, but sold out a serious contemplation of his morality to get that. Then, once there was no more profit to be had off the fun show that reveled in homicide and irony they tried to Make a Statement on the way out the door, giving an ending that satisfied neither vision of the show.

Breaking Bad - Excellent. In some ways overshadowed by the preceding episodes, it was satisfying, but in a way that was earned, and appropriate. The show was always absolute in its morality, and the triumphs of the finale were earned by a degree of repentance.

The Shield - Excellent. The triumphant flourish to a tense season that ended on a rising note, which remained true to the main character's ability to keep going, while at the same time finally addressing and explicitly portraying him for what he was and forcing him to confront himself and his actions.

The Wire - Great. Serviced its themes, wrapped up character arcs, while showing that the game still goes on, with new players stepping into old roles, and a bunch of tiny triumphs that were really earned.

The Office - Pulled a horrible last couple of seasons out of the dive at the very last moment, but still a rough landing. The pity is that at the very end, they showed some signs of things that could have been interesting, if they had not wedded themselves to keeping as close to the way things were with Steve Carell. They made Andy into a Michael Scott II, and he was horrible, tiresome and insufferable, with none of the redeeming features of Scott's character (which were thin enough for me anyway). It was in the last couple of episodes or so that they remembered how much fun Jim & Dwight are when they are done right, and I will always wonder if that was a case of a road that should have been taken much sooner for a better last three seasons or so, or if it was a case of less is more.

Most other finales that come to mind don't really stick out for me. They were an ending. The story went on and then it stopped, such as with Rome or 24. Others ended, but their ending was more like a victory party or farewell ceremony than the conclusion or climax of a story (Scrubs and Chuck spring to mind), which is more of a meta thing than a "good" or "bad" ending (on that note, I kind of liked what HIMYM did, having their equivalent of an epilogue before the finale). Some shows, of course, ended without a finale, just a last episode (The Unit, Terriers, Veronica Mars). Others were wrap-ups at a point where it was starting to wear out (House MD & Alias, for example).

Then there were some that were a final bad episode of a show that got really bad at the end, like One Tree Hill. My brother and I binged-watched the last half season, mocking and ridiculing it the whole way.

Another case I can't decide how to classify was Prison Break. The title and the premise of the first season were spectacular and the second season was a natural follow-up (the characters are out of prison and on the run), but there isn't really any place you can go from there and still be true to such a specific title. Season 3 they tossed a bunch of the characters into another prison, with a new challenge to break out, which was curtailed by the writer's strike. Then the final season, they came up with a new story that had really no reason to be called "Prison Break" but which I felt played to the strengths of the show, mostly by having enemies forced to work together, and alliances of mutual interest becoming the basis for something more. It got a little too heavy into its own backstory and the improbable hostile foe, with inconsistent portrayals (it turns out the vast invincible & ruthless conspiracy has a weakness that can be solved by acquiring all the McGuffins components! The main villain has suddenly abandoned his cool affectations that made him so mysterious and compelling in his handful of brief appearances in season 2 & 3, and once we know more about him, he's really not impressive), but the interactions of the characters we had become invested in by now were still worth watching. And then, in the final montage of the characters and their fates, there is an unforeseen twist in the last shot. Several months later they had a two-part TV movie that showed how they got from the first half of the final episode to that actual ending montage. It was an okay story, but the unusual format made it hard to consider on its own merits.

There are probably others I can't think of right now, but if I can think of something worth adding, I'll post a reply to this one...