As for the Wii, definitely not worth it. It's fun at first because it's so different, but after awhile it gets boring.
They threw out all their big titles so soon, and all their 3rd party stuff is junk, the graphics are horrendous on some games, and for the most part they're only fun with a group of friends.
Now with Fallout 3, PC and 360 get Downloadable content. PS3 does NOT get that. But only the PC version gets the G.E.C.K, which is the construction kit. So if you have a PC that can run Fallout 3, get it on that.. If not, get a 360 if you're big into those games.
Gears of War 1/2 are okay games, but definitely not huge huge sellers. For the most part, only good for 1 playthrough each.
Mass Effect was horrible in my opinion. One of Bioware's worst RPGs yet.
Left 4 Dead is also gonna be better on PC, because of the modding community. There's already some amazing maps that are due to be released soon, so if your PC can handle it, get it on PC.