I didn't think Mario Galaxy was that great. The game mechanics were good, and the general ideas, but the world's weren't that creative or fun. That's one of the things I think that made the first Banjo Kazooie so great. They had great level themes, which led to great level designs, which led to great level challenges.
I LOVED Super Mario Galaxy. That was the 2nd best game of last year in my book, next to Bioshock. In fact, it's probably in my top 3 as far as Mario games go.
Banjo Kazooie remains as a top 5 favorite to me. Oddly enough, I never got around to getting Banjo Tooie.
Maybe not my Top 5 but like you i still liked it but never played the next one. Although Sequels on the Same console are rarely better (Excluding Sports games) I'm pretty stoked for this though. My Games list is Huge ATM >Fallout 3 (Xmas) >Banjo Kazooie >Midnight Club: Los Angeles >Prince of Persia >NBA 2K9/Live09