I just finished this game, playing together with my brother, and we had a blast. (Surprise twist: we're both in our forties.) 

I think all the levels can be finished when playing alone, but with two players it's easier. Or is it? If you're not communicating and following a plan, you're sabotaging each other just as much as helping, and that's hilarious. 

Anyway, there are eight worlds with ten levels each, and a lot of different puzzle mechanics that are introduced and explored nicely throughout these worlds. It's an entertaining puzzle action game, with a lot of variation.