If nuclear wasteland and Bethesda don't spark your interest, I have nothing to say to you.
Fallout 3 has the same structure as Bethesda's other huge hit for the 360, Oblivion, but it features a lot of improvements. Most notably are the graphics, which look even better than Oblivion's, and the game runs much smoother in the open world segments than that game aswell. I also greatly appreciate the new camera control, as it makes it much more natural and easy to go from 1st to 3rd perspective. The Fallout 3 world is also just as large and expansive as Oblivion's realm, and it contains a ton of bad guys and sweet loot, ripe for the taking. I also thoroughly enjoyed the story, but that is basically a given when you are playing a Bethesda game.
I do have a small list of negatives although. My biggest gripe would be with the free aim system. When you aren't using V.A.T.S. (feel free to look it up if you want more details, but it is basically the main tool you will use to decimate your enemies) the targeting is kind of iffy. Even in first person, it is very easy to miss a target in free aim because of the way the weapon fires and the fact that there is no sticky targeting. I'm not saying it is impossible, but it takes some getting used to and it is definitely not as good as other first person shooters, which I suppose this game is not, but it is still disappointing.
My other biggest gripe is the level cap of 20 and the definite end of the game. Unlike Oblivion, you cannot play "forever". After the main story line, that's it, game over. The level cap is just annoying, since Oblivion never had one either. I believe there were more skill categories in Oblivion however, so that may explain why there is a cap, but regardless, there is expansion content slated for March that will raise the cap to 30 and allow you to continue to play.
So, long story short, buy this game, because it rocks very hardcore. Thank you Bethesda!