This game is my game of the summer, according to my 3DS diary I have more than 20 hours on it, more than Super Mario 3D Land despite 3D Land making you do everything two or three times (maybe some of the time is from suspend mode, though, I don't know if it counts).
It's very easy to think it's mediocre or forgettable: the Pipe Dreams/ Pipe Mania mechanics seem stitched on the Minis, the 3D graphics should be a lot better since there's so little to display (it's not even at 60 fps), the minigames are shallow and boring, and the whole game effectively plays on the bottom screen and looks like an IOS $1 game, when it's here sold at $10.
But the rules of each mode are varied and perfectly fine tuned, the level design is bloody brilliant (the user created levels are abysmal compared to it), and God bless Nintendo, it's at last
HARD from the beginning, you don't have to spend more than half the game on easy tutorial levels like in so many other Nintendo puzzle games (and more specifically Mini-Land Mayhem). Here, the mechanics and tiles are all explained very quickly without filler levels or (another flaw of other Mario vs. DK puzzle games) stupid boss level, you're free to play tons of spectacular quality levels from the very start without having to wait "for the good bits".
I'm near the end of the game, and discovered the game adds "expert" levels in Mario and Peach mode once you finished the "normal" levels: 10 more nail-biting levels in Mario mode, and 20 "smoke will pour out of my ears from thinking" Peach levels.
This game is up there IMO with Pullblox and Fallblox among the best puzzle games in recent years. It nails the main quality of a puzzle game: being in appearance completely simple and innocuous, but in reality devilishly challenging, which makes you mad at yourself that you can't solve something that seems so simple, hence motivation, hence addiction, hence satisfaction when you finally beat the thing.
@ZeroYou have to use the trashcan mechanics. I see you don't mention it in your review, but if you make a loop in Mario or DK mode without a mini on it, it creates a trashcan. Along with creating a loop with a mini on it raising the tiles (making your mini reach coins or keys) and adding time bonuses, it's a carefully thought out and planned mechanics that makes the game much more interesting than other Pipe Dreams clones.
Also, the variety between the four modes is very welcome and surprising.