So, the dude who does Zero Punctuation has a pretty spot-on review of Fallout 3 (warning: naughty language... put the headphones on). I just wrapped up the game, and liked it a lot.
It's kind of like a mix between a first person shoot and an role playing game. You have the option of calling your shots with the V.A.T.S. system, or if you're set for ammo and have the twitch monkey reflexes you can just use the crosshairs and score your own headshots.
There's quests to run, and different factions (basically towns) that you can build rep with. Aside from a few core missions that move you along the story line, everything else is just kind luck-to-find. There's a surprising amount of stuff to explore in the game, and I found the levelling up part to be practically unnoticeable. I would recommend that you invest early talent points in stuff like lock picking, science, explosives, repair, etc instead of going for nothing but weapons and stats improvements. The game becomes a lot easier once you can "hack" into any computer (that's basically just a game of hangman where you guess the password) and pick locks. Also, figure out how to repair stuff early on in the game... you'll save a lot of money and improve the amount damage your weapons do.
The moral choices in the game are also interesting, in that they affect future quest opportunities later on. Much like the decision to go carnivore in Spore, I ended up going Good-Guy in FO3, which actually ends up causing more problems than you'd think as bounty hunters are out to get you, and you lose a couple of support options early on in the game.
Overall, though, it was well done and worth the price of the game. Thumbs up, Bethesda, and thanks for showing me around DC. ;)