Sounds like I'm enjoying the single player more than you. Yeah the levels are short and linear, but I like how they keep throwing things in to mix it up (sponge blocks, invisible platfotms, etc). The levels feel comparable to Mario 3D World in terms of their length and how they mostly seem to be tiny areas connected by pipes/tubes. Obviously not even close to the platforming bliss that game is, but still solid. I'd be interested to see them expand on the campaign on a sequel.
Multiplayer is fun. The small selection of maps is a bummer. Hope they add more at a decent rate to keep me coming back. More modes would be nice, too. Still only have the one unlocked, but the matches are over a little too quickly, IMO.