Best Animation and Environments: Monster Hunter Tri
Best Effects: The Conduit (but only some parts of the game)
Best Visuals in very complex scenes (Lots of Objects, Expolsions...) CoD: WaW
Best Overall Design: Mario Galaxy
Best Texture Quality and Light Effects: Silent Hill: SM
Its very hard to say what is the best looking Wii Game by far... There are many Games with good Visuals and there are some games that look very good in some parts and much poorer in other parts. Dead Space: Extraction, RE4 and RE: Dardside Chronicles are beautiful games as well, for example.
I Dont understand why some people say Red Steel 2 has great Visuals on the Wii. I really liked the game for its controls, but the Visuals are much weaker than in the other games i named here. Im playing on a Sony Bravia TV in 480p, so maybe it looks better on an oldschool TV. SH: SM for example has the Texture Quality of a XBox 360 Game in 480p. I Have never seen such Sharp Textures in a Wii game before.