Think ps2 content, gamecube graphics, and a new wii control scheme, and you have one of the best wii games out there.
Graphics - When this game came out on the gamecube back in 2005, it was a damn fine looking game, and one of the best looking on the console. Now 2 years later... it still looks good, but defiantly dated by todays standards though.
Sound - Amazing sound design all around. The voice acting is kinda lame, but the slightly retarded sounding villagers to the moans and groans of the zombies, everything sounds amazing, and even creepy at times. It just creates a great atmosphere.
Gameplay - This is a port of a two year old game, so there not many gameplay changes, but there is one major one: the wii controls. And they work pretty well. Aiming is way easier in this version I thought as opposed to the gamecube and ps2 versions. I did have some problems with the game and aiming with my wireless sensor bar, but it was very smooth and fluid overall.
Value - You have a main story that clocks around 8-10 hours to finish, but theres a good chance you'll go back and replay it a few more times. Theres also a harder difficulty setting you can unlock, a separate story line called (insert pun here) "separate ways" which can last a few hours by itself. Also a few other modes, which are pretty fun.
Overall - I was very surprised by RE4 wii, mainly because of all the other half-assed wii ports out there (splinter cell, far cry, etc...) but they really knocked one out of the park here. I would have given this game a perfect score if they updated the visuals and added more content, but by itself, this is a must-buy for wii owners, even if you've already beaten the game.