My review will be a little late, but it's a fantastic game. You can tell Retro still had a lot to give to the franchise, the level design is absurdly good, the levels are longer and filled with ideas and no two are alike. The progression and pacing is a thing of beauty, excuse the cliches, but some sections are very gripping and kept me on the edge of my seat.
The music is, of course, brilliant and the graphics are clean and detailed with fluid animations. Never spotted a drop from 60 fps, but I'm not the most eagle eyed of players. Loved the artistic direction and the enemy design is great, better than Tikis that were just passable in my book and much better than the kremlins, which I find atrocious.
The game is definitely geared towards single player, it's good to have the option to play with a friend, but the system is a bit more complicated than it should be, dropping in and out isn't as simple as in Mario games. Loading are long, I'd say usually around the ten second mark, but I only timed it twice, one I got 10 seconds and the other time 14 seconds.
It's a pure, no bs, 2D side scrolling platformer and a brilliant one at that.