Having finished MP3 last week, I decided to bust out the original MP and have a go at it since I quit around 24% into the game. Here's what I noticed:
1) Anyone who says that MP3 has slightly upgraded or similar graphics is blind. MP looks muddy in comparison, and has more aliasing and I found some of the enemies difficult to distinguish from the background because of the low-res textures.
2) I have been spoiled by the Wii remote. The aiming and movement in MP3 is fricken' unbelieveable. MP feels strange, and not being able to look around with the remote while moving with the thumbstick flat out sucks. MP feels old fashioned and clumsy in comparison. Actually, I was mucking about in GoldenEye today, and that also feels clumsy and slow.
3) I don't know what the framerate is for MP, but it's probably 25-30fps with dips here and there. As a result, I had to quit early because I was getting nauseous. MP3 gave me nausea on occaision, but I basically had to stop playing MP before I threw up.
I know that MP gets raves and is usually the highest rated GCN game, but I don't know if I will ever start it up again.
I would consider MP3 GOTY just for the controls. It wipes its ass with dual analog.