Didn't care for Sticker Star, but I was told to give this one another shot, and I'm having a decent time. The presentation, writing and ideas are some of the best the series has had to offer, but every positive aspect is usually accompanied by a negative one.
The battle system was one of the parts I disliked the most in Sticker Star, and not a whole lot has changed here. It's my most disliked part here once again, but some of the more egregious issues have been alleviated. A modicum of character growth has been re-introduced to the combat, by letting you earn paint-hammer-EXP. It's a baby step, but it's something. Another fix for the combat, is making coins easy shockingly easy to obtain. I hit the maximum capacity in the middle of chapter 2, and wasn't sure exactly how or why it happened. What this did though, was make me want to spend those coins. I'd buy the best possible cards available to me in bulk, and this allowed me to comfortably end every single enemy encounter in a single turn since. This is in contrast to Sticker Star, where I hoarded my best stickers, and I was too stingy to spend my money on them. This made these pointless and slow battles go even slower.
There is one part that really bugs me though, and that is with how the game deals with game overs. Rather than letting you retry a stage, it boots you back to the title screen. I understand why other games with manual saves would do this, but Colour Splash saves every single time you go to the overworld. A simple "Retry" option that boots me back into the stage from the start would carry the exact same consequences as booting me back to the title screen and making me re-select the stage from the world map. It would just cut down on the tedium. There have been several timed sections now that give you instant game overs, and those don't need the extra help being un-fun.
The game has so many flashes of greatness in it, that it is all the more disappointing when you get the constant reminders that it isn't as great as it could have been. Paper Mario is in a weird place where it is arbitrarily shackled, and it saddens me. It kind of makes me want to stop making these, so they can put their excellent ideas to use in a series where they won't have to limit themselves due to internal politics.