I agree totally with rnlf. I loved the sprites, particularly the little red and green guys. The bigger blue and purple ones confused me though. They didn't seem to do anything- the blue could just be deleted and the pink replaced by a wall and there would be no difference.
The jumping also felt a bit off. I think rnlf's comment hit the problems pretty squarely though. In addition, I felt that the maps were poorly designed for the type of jumping you had. I was constantly hitting my head, and the walls were always at the maximum height, so it was very hit or miss whether I hit it just right to get that double jump. For a game so focused on jumping, a few areas that were more open would have made it far better.
In addition, the squid things shot as soon as you got close enough. Most places, this was fine, but near the very end, you had to have more than 1 hp or you would instantly lose because going up, it would always hit you. There was a similar issue with a few of the red guys on single block that were at the max height of your jump. It was extremely difficult to slam them without them hurting you. Platforming is so skill based, attacks that always hit you, particularly at the end of a level, just feel really cheap.
Also, it looked like there were alternate paths a few times, but I could never use them. Maybe it was not understanding the blue/pink guys, but if you were supposed to go through those, I couldn't