Ultimate Alliance has great replay value and extras, on top of that it takes a long time to beat. The best game for the Wii (IMO) right now, then Sonic (I don't have it, i'm guessing), then Elebits or DBZ: Tenkaichi 2.
Get SSX Blur or wait for Super Paper Mario. Blur is great once you get the controls and paper Mario looks like it is going to be the next great game from Nintendo.
Marvel is a fun game for multi players. For me it took less than 20 hours to complete. Fun game but should have been way longer. Tiger Woods 2007 is a great and fun game. Excite Truck is one of the best games out for the Wii IMO.
I have sonic and its a good game. i went out and got rayman yesterday and im not regretting it! not sure what game to get nexy but think im gonna wait for a mario game !!!!