Picked up Captain Toad over the weekend and played through Book 1, which is the first 18 or so levels. This is an enhanced version of the Captain Toad minigame levels from Super Mario 3D World. The stages are larger and more creative and there's enemies that will rush at you and try to kill you. You can't jump, so you have to either run or toss a vegetable at them if plants are nearby. You can fall off ledges to stomp enemies, though, plus if you touch enemies on the Wii U controller screen, you can freeze them in place and let Toad run by. Levels are mostly action-puzzle based and have been pretty easy for the most part.
You maneuver Toad through levels to get to the star at the end, but also can pick up three gems hidden throughout the levels. You have to get gems to proceed to later stages and also to play bonus levels. In addition to the gems, every level also has a secondary objective that does not reveal itself until you clear the stage. This might just be collecting a certain amount of coins or getting a hidden 1up or golden mushroom, or it might be something a little more challenging like completing a level with manually-controlled moving platforms in a certain number of turns, or getting through a level without being seen by Shy Guys. (Yes, stealth levels. In an action-puzzle game.) There's even boss levels and fights, which play very well.
If you have save data from Super Mario 3D World, you can also unlock and play through entire levels from that game as Toad. I've played two so far and they were kind of boring. Unlike the main game, these levels aren't tailored to Toad's movements and all you do is walk through them, collecting coins and avoiding a few enemies. Feels very tacked-on without any kind of puzzle elements present.
The controls are very simple and work well. You generally just move/run and pick up items in levels, but occasionally you will need to use the Wii U gamepad's features to move blocks, turn switches, aim cannons, or move platforms via the mic. I found myself generally just playing this game on the gamepad screen and ignoring the TV because of it. One annoying thing about the controls is that gyro-aiming can be used and cannot be turned off, leading to the camera being inadvertently moved when you don't want it to be.
Overall I'm glad I picked this up, but the game still feels very much like a mini-game and might have been better-suited as a $20 downloadable title instead of a $40 retail release.