I will admit that looking at New Super Mario Bros. Wii, I was rather unimpressed, even though I really did enjoy New Super Mario Bros. on the DS. I think it may just I would have preferred a more single player focus rather than the multi-player co-op gameplay they seem to be going for. It doesn't look bad by any stretch, just not something I'm all that excited for.
Galaxy 2, though, is definitely something I've wanted since I've played Galaxy. Mario 64 is still my favorite platformer, and anything Nintendo does to incorporate aspects of 64 can only be seen as a positive. One of my favorite things in Mario 64 is how open-ended it is, and how you can basically get Stars in just about every level in whatever order you want. Galaxy was great, but the linear gameplay was a bit of a turn-off for me. I'm not exactly sure I care for the addition of Yoshi or even want it, but if upping the difficulty and making the levels much less linear are definitely things I wanted to see in the next Mario platformer.
I think Pikachu is cooler than Yoshi.
