One of the best platformers I have ever played. The Donkey Kong Country series was the one I always considered the best, until I tried this one. The main thing I like about this game, is that you move at a much faster pace, compared to something like the DKC games. There are optional challenge levels that will test just how good you are at controlling your character at its max speed. If you can complete those, you earn the right to play the Land of the Livid Dead level, which is the most challenging stage in the game.
All the secret/bonus rooms in a stage, have their own unique platforming segments that you must get past, in order to get the reward from it. I enjoy that a lot more than how the DKC bonus/secret areas usually are (just collecting the bananas). The boss fights are also a lot more difficult and better designed. The art and animations make the boss fights look so good and those water stages also.
The difficulty is also great. Nothing is cheap and unfair. Everything stays the same for a stage and you will never feel like it was the stage's fault for dieing, but your own. The game also has fast respawns for when you die and automatic checkpoints per stage. You will never have to start back at the beginning of the stage (unless you die there) and you will get to keep everything you have collected so far.
The game will last you 10+ hours, if you plan on trying to unlock all the levels. If you like this game, then check out Rayman Legends, which I think is even better.