Season 1 was excellent, I liked Season 2 although it seemed to go a little long before wrapping it up. Season 3 was ok, enough to keep watching to see what happened in Season 4. Some people didn't like Season 4 but I thought it was pretty good (it revolves around witches).
Season 5 was atrocious, horrid garbage that should have never been produced. It jumped the shark in a major, major way by bringing back the main villain killed in Season 3 and then the plot was just bad. The creator and showrunner Alan Ball was leaving the show and so he decided that he would "explore" religious fanaticism in the context of fanatical "vampire religion". I honestly think he knew he was gone and just didn't give a shit about the show anymore and just put together something to fulfill his obligation. The entire season was just B-A-D.
So, Season 6 a new showrunner took over and was screwed because Alan Ball decided to leave the show with this lame plot direction. Amazingly, the new guy redeemed the show somewhat and made at least a palatable season.
Season 7 (the final season) has started now and I only watched the first episode but have been too busy to catch up. But, basically the show is still really screwed because of the lame direction Ball sent it in when he bailed.
Frankly, I will watch this last season since I've watched the prior seasons, but I think the show really jumped the shark in Season 5.

To sum up, if you really liked the genre and stuff, I would say go ahead, but it really doesn't sound like that, so I would say you should probably skip it or at least stop at the end of Season 4.