Just Dance :D

Easily the best game on the Wii this gen. Either that or the second.

Monster Hunter Tri

No more heroes 1 & 2... Honorable mention to the house of the dead overkill, Agent washington and G are a blast!

Iwould have to say that so far it is Lost in Shadow.

Xenoblade is actually a second party game. (Though I might be first since I think they own 100% of the developer Monolith Soft) EDIT: Yes it is a first party developer. http://en.wikipedia.org/wiki/Monolith_Soft

It is pretty hard to say there are just too many:

Ookami, Lost in Shadow, de Blob, Monster Hunter, No More Heroes, House of the Dead: Overkill, Little King's Story.

Okami but that's a PS2 game haha

Not that much to choose from for me, so Goldeneye easily takes it, i still play. HOD Overkill comes second

I'm going to be boring and say MH Tri, but I have also logged a lot of hours on GoldenEye.

I know it was on PS2 already, but it has to be Okami. The game was absolutely fantastic. The style, music and gameplay all came together magically.

The Trauma Center series. It was one of the first 3rd party games I bought (together with TP and RE4) and I really enjoyed it, felt very fresh. Had even more fun with the sequel's co-op and the updates in the import brought in a slew of other specialties!