If you liked SMG2, then yeah, definitely. It is a bit easier but it's clearly different (other than the obvious "you play as Mario and go through these galaxies to get to the end" and a few levels are similar, but it's still a completely different game), and just as fun. :p
Ice Cream Topics Gotten to 500: 4 Lots of ranting and stupidity: http://www.gamefaqs.com/boards/922345-Sparx's_Awesome_Rant/64829504
I did the same, and I would advise against playing them back to back: wait until a year at least has passed, or you will not enjoy it fully. The reason being that Mario Galaxy 2 is very thorough in using its formula to the fullest, so you would feel annoyed by the many training levels and indifferent before the many recycled elements. Don't get me wrong, a platformer game is its own levels: Mario Galaxy has a load of masterpiece ones, but you really want to look at them with a fresh mind.