Lack of split screen multiplayer. Multiplayer=online these days. But there's nothing like playing with 3 others at home, drinks/beer, nibblies, trash talk and hangin' on the losers.
Its why i like Nintendo consoles. 4 player split screen built in from N64 days. Goldeneye multiplayer on N64 was great as was Mario KArt, theres some great 4 player games on Gamecube eg Mario Kart, 007 Nightfire, FzeroGx, Smash Brothers, even Fifa.
Just bought a Wii today and son's having fun with two other mates getting to grips with it.
Hell I'd settle for two-player split screen.