Best Mario in the franchise hands down. It continues directly from galaxy and added much much more diversity. The game is simple enough for all ages to play, but obtaining the stars and other collectibles satisfies the hardcore (like myself)with unique scenarios and impressive difficulty.
I only recently played the first Mario Galaxy and absolutely fell in love with it. It is one of the most polished and amazingly stylized games I've ever played, and with fresh and inspired game play in each galaxy. So of course I was excited to get my hands on it's sequel. I went into playing this game with very high expectations, and was sadly disappointing. I'll start off by saying this is in no way a BAD game. just a bad SEQUEL. Although this game has 3 times the upgrades and abilities, it still feels some what lacking. Maybe it's the absences of the amazing hub world from the original, or maybe it's the repetitive, uninspired worlds. There are honestly at least 2 copies of each galaxy, making it feel like you're just going through the motions. Also, the plot line is literally the same from the original. Even with the addition of Luigi in this one, you can only use him in rare conditions and his controls are just so slippery, you'll be slipping every where, which gets pretty annoying. If you're planning on playing the Mario Galaxy series, i definitely suggest Mario Galaxy 1.
If you've played SMG1 before playing this one, you will know after playing SMG2 that this has some serious faults when considering new and unique features. 90%+ of the time playing this, I felt like I was playing the first game of the franchise, but with a extended bonus pack.