Hostile Creations:
It really depends on how much you liked the first game. Here is what the new game adds:
1)Each level has an additional Star. This Star is usually of one or two different varities of challenges. Hit a Star Switch and Race through the level to the Star: Or collect 5 Silver Stars within the level. One is more of a puzzle and you must know the levels. The other is a new kind of Scavenger hunt. Both are pretty enjoyable inclusions.
2)In Some Levels (Not all) Red Coins have been moved around so you kinda have a fresh experience trying to find all the Red Coins. At least I think this is true, because often I found red coins where I didn't remember them being.
3)New Mini Levels. There are about 4 new mini levels within the game. These levels are much shorter and only hold 1 or 2 Stars each. They all feel unique, and they definately add to the experience.
4)New Bosses and Sometimes New Ways to defeat Old Bosses.
5)Really Addicting minigames. Yes some of the mini games aren't as good. However, you will find yourself addicted to atleast 5 of these minigames, and they are great fun as a short time waster.
6)New Characters. Now this is a toss up. The new characters actually make the game much easier and much more forgiving. Luigi and Yoshi's flutter jumps make timing jumps much easier. Yoshi's Egg attacks are also too powerful for the game. There really isn't a drastic enough difference to change characters too often. Just stick with Luigi. Wario however is worthless, except for stars that require him.
7)The little surprise touchs. The most fun I had with this game is the little added touches. Some levels its new enemies. Others its the addition of a green turtle shell or the owl. But the levels aren't exact copies of the originals, and the additions are very cool to run across.
To me all these add up to a game worth revisiting. The new stars give you more challenge and gives you enough new experiences to not make you feel like you are just playing the same old game. Nintendo was real smart in spreading these stars among the levels that already exist, because you get to the new stuff much quicker.