Variety of types of stages
Fun new battle style
Option to collect items
Well done 3D
NOT SO GOOD:
Confusing series of events, not enough hints (a walkthrough is helpful at times!)
No explanation of absence of leveling up
Paper Mario Sticker Star has a lot of cool features. The worlds are beautiful and explorable (not side-scrolling), and the character dialogue is very well written (the Toads are hilarious). The battle style is really cool- you pluck stickers on your journey and add them to a sticker album, and in battle you can use the stickers to make an attack that you can make more effective by timing and blocking during execution. Players who like to collect things will have a good time finding every type of sticker and "thing" (objects which can be turned into stickers and used for special purposes in the game). Collected items can be added to a sort of museum in the game, so it becomes addicting to collect them all. The stages of the game are not monotonous, because there different twists thrown in here and there, so you aren't constantly engaging in battle after battle.
The 3D in this game is one of the best utilizations of the 3D I've seen so far on my 3DS. Cut scenes are good to watch with 3D, as things really pop. Also, I was surprised when playing a wintery level and snowflakes began falling in believable 3D.
My only complaint about this awesome game is that there are not enough hints for you to know what to do. Often there is a very random task that needs to be completed, and without a walkthrough to read you might wander around aimlessly for a long while in frustration. "Secret" rooms are often NEEDED to progress in the game, and you often need to carry with you a specific, one-of-a-kind sticker to beat a level with no hint that it would be needed (so you need to backtrack and find it before you can complete the level). Your guide, Kersti, will give you hints, but they are often vague and unhelpful. Also, some players might be confused to find that there is no real leveling system for Mario- instead, you collect HP up (heart) pieces to increase your health-bar, and as you progress you also get new stickers that make your attacks more powerful.
Overall, the good very much outweighs the bad in this case. Paper Mario Sticker Star is one of my favorite Mario games. Full of funny surprises and cool stuff to collect, I highly recommend it.