It really is better than the first one, I think. It takes everything that was successful about it and expands upon it, with new game mechanics and enemies in just about every single level.
One of my favorite features is the new "faceship", as opposed to the home ship that was used in the last one. Everything about it feels so vibrant and alive, and with the fantastic music playing it's just about impossible to not be happy while you run around. The addition of Yoshi is awesome as well, and he makes room for a lot of awesome new mechanics, like the hot peppers in the second world.
And then there's the new galaxy/planet navigation system that's very similar to the layout used in the NES and SNES games, allowing you to access every galaxy and every planet from one interface, without having to run all the way across your ship.
And of course, just as in the first game, the controls and camera are smooth, the graphics are vibrant, the soundtrack is fantastic, and the level design is incredible.
It's also worth mentioning that it has a 98 on Metacritic, with 10s from GameSpot and IGN, as well as dozens of other sites and magazines.
i like orange