One of the biggest flaws is the battles and stickers. The battles have very little value other than collecting coins and maybe some valuable stickers. Not enough of an incentive and I find myself avoiding the battles because they can be super annoying and deplete your stickers.
If it wasn't for the fact that the battles don't give you enough rewards in the way of building your character then I wouldn't mind the battles at all. They are enjoyable and the stickers are a interesting way to battle.
Boss battles are a chore as well and thing stickers are shoe horned in the gameplay. The very few times I've been truly stuck I looked at a guide and avoided hours of trail and error. Made the game much more enjoyable and I only looked at a solution about 2 times in my 20 hours so far.
Now to the positive. The graphics are great and really gives you the idea of paper and cardboard.
The music is also great with good remixes of old classics.
Gameplay even with flaws is addicting and has the collecting aspect with the secret doors and the sticker museum which challenges you to collect all the stickers in the game and even achievements.
Characters and dialog have that great Paper Mario charm as well.
My biggest gripe would be the boss battles. You have two options when fighting: Find the one sticker somewhere in the current world to make the boss battle super easy, or don't use the sticker and struggle to even dent the boss. The "key item" aspect to the bosses shouldn't be mandatory, they should simply help.