I have just completed the 6th level, playing it on my notebook via keyboard. The game is great, except two points. In level 1-5 there is a high jump, which is almost impossible to perform with keyboard. Tried more over 100 times (really). And then the boss at the end of level 1-6... probably the most annoying boss I ever met. It is absoultelly unclear how to beat him. I finally did, but I am not sure how. Took me more than half a hour and I lost about 50 lives there, fortunatelly in adventure mode there are unlimited lives. The boss looks very nice, but it is a pure pain to fight him.
I will buy xbox controller probably, especially for this game, which is really good. But few points should be adjusted I think.
And the soundtrack is just superb. I have it in my car at the moment, listening while driving to work.