Fallout 3: Crash City
This could have been a great game and it may yet become one. The game play is immersive. The reviews at this site capture the feel of the game. The only point I haven't seen mentioned is that the game is in reality a giant maze. While you can see all the places you're supposed to get to most of the streets and roads are blocked off - this is especially true in DC - so the player has to do a lot of trial and error wandering around to find the destination he's after. Once found, however, you can teleport to that destination and avoid being the rat in the maze.
The reason I've ranked the game so low is that it was released prematurely. It crashes regularly. I've made all the fixes Bethesda advised and many others found on various forums and the game still crashes. I have a new computer with high end sound and video cards, 6 GB of RAM running on Vista 64 (it seems to have a lot of trouble with 64 bit Vista) and the only was I can get the game to run for about 30 minutes is to play it in a window with every game setting turned to it lowest value. The game has crashed according to the Windows log 100 time over the past week. After a crash rebooting buys you another 30 minute. Seems like the game has a problem with memory leak in addition of the problem mentioned with codecs. The game plays better on my seven year old computer than it does on my new one. The old one just meets the minimum requirements for the game and is therefore set to the same setting I have to run the game on the new machine at.
So unless you want to become a regular correspondent with Bethesda's technical staff I'd wait until a patch that fixes the crash problem before buying the game. Do a Google search for "Fallout 3 crashes" and you'll see how many people are having problems with this game. To be fair this does not seem to be a problem with every user.