It's a fun game. There are a lot of annoyances... weapons and armor (especially helmets) break way too quickly, the minigames are fun for a little while but are used too much, the ending sucks majorly, there isn't a big enough variety of weapons, and SPECIAL stats don't seem to matter that much. I also wish VATS were a true turn-based option - not required, but an option where you and all your enemies get turns to attack. Basically, just like the old games. It wouldn't be required but right now it's too much like bullet time from Max Payne. Max Payne's bullet time made you invincible while you were in it, just like VATS.
Thing is, though, while I agree with many of the criticisms people here have made of FO3, I still think you guys are overreacting. People here seem like they were already certain they would hate the game the moment they heard Bethesda was doing it, and now that it's out, every little problem gets blown out of proportion. FO1 and FO2 had their share of problems too... a huge number of them, in fact. But they were still good games.
As far as how well FO3 stays true to FO1/2, I guess it's not really outstanding in that regard. The art direction in FO3 is great - I think they really nailed the post-apocalyptic atmosphere and did a wonderful job of translating the low-resolution, 2D world of FO2 to a big, interactive 3D one. However, there are just too many traces of Oblivion in it. Character animations are bad, AI pathfinding is bad, Fast Travel isn't nearly as fun as FO1/2's travel system with their random encounters, and I don't think there's enough variety in the enemies (same with the weapons, as I mentioned earlier).
As a Fallout sequel, it gets it half right. It has the atmosphere and some of the tongue-in-cheek humor, but it lacks the tactical combat and much of the "soul," if you know what I mean. As a game itself, it's great. I've been enjoying it a lot.
The biggest thing I hate about the game is the ending. Total crap. I've never seen a worse ending in any game.