It plays to both the great strength and weakness of the system:

Veteran gamers will find a rigorously researched and playtested rule for nearly every situation they can conceive. Tell the GM in your AD&D campaign you want to play Han Solo and try his blaster against a dragon and he'll probably slap you; tell your GURPS GM that and he'll tell you to come up with a good character story, spend, say, 30 points on the Unusual Background Advantage and remind you that 1) dragonhide has Damage Resistance 5 (-5 damage) and Passive Defense 3 (+3 to block/parry), 2) your blaster does 4d6 damage and 3) you won't be able to recharge it after you drain the battery. Also, while your Piloting-Hypership skill of 27 is very nice, it's also very expensive and next to useless in Camelot. You can and are encouraged to homebrew if you want; if it's a really good and useful rule, send it to SJG and they might credit you in a worldbook. More often than not though you'll probably find (if you look) that not only is there a rule for it, but it's better balanced and more realistic than the one you had in mind, 'cos a half dozen SCA members and a couple fiction authors argued and playtested it for months.

That's also the great weakness though; as Isaac notes, it can be imposing to beginners and VERY imposing to inexperienced GMs. My advice to first timers would be to concentrate on the character creation rules, especially skills and attributes, and let the GM worry about the other rules; if he's not up to that your game's going to collapse anyway. Of course, the GM has other problems; there's no fixed game world (they did provide Yrrth as the generic medieval setting, magic optional) and since there are no classes all they tell you about clerics is to make them take the Clerical Investment advantage and decide what spell colleges you'll allow (they did put a basic "evil" and "healer" cleric in a sidebar, but you get the idea). Creativity isn't just encouraged in GMs; at times it's vital. Of course, that's true of any good GM anyway.

The good news is GMs have the freedom to do whatever they want; the bad news is they're often responsible for doing just that.