I'd have to say Returns blows NSMB Wii out of the water by a good lightyear.
When they announced NSMB Wii, I was hoping it'd turn out to be something like DKCR, but I had to wait for Returns to come out to actually get exactly what type of experience I was after. That being: action-packed levels, gorgeous visuals, scenery continuity (I'll explain that if you want), actual camera-work, about 4 trillion unique ideas, great music, nostalgia by the ton, and hard as all hell. It's almost controller-breaking/throwing hard. DKCR is well worthy of its version of the Super Guide because if you suck, you'll most definitely need it. Going back to action-packed levels, in NSMB Wii, there might be 1 or 2 levels I like in an entire world... maaaaybe 3, but there's approximately 0 levels in DKCR that I don't like. It never drags.
lol @ Miyamoto or whoever saying online multiplayer for NSMB Wii wouldn't be possible because the game was pushing the Wii to its absolute technical limits. I mean, yeah, it does have a crap-ton of levels, but visually, I'm not seeing where it's just taxing the system so much the thing starts smoking. DKCR, I feel confident in saying, is [darn] near the Mario Galaxy of side-scrollers, visually. There's a lot of depth and vividness, an incredible amount of detail, and the island feels very alive. The pre-rendered stuff is equally amazing.