Once in a while, my character suddenly dies after touching a block, even if the are no spikes around. Speaking of the spikes, there's something wrong with collision detection, and sometimes it's rather hard to calculate safe distance before making a jump (and that kind of precision is necessary on some of the levels).
A few general notes: graphics are simple but sufficient for this kind of game, but for the audio... let's just say that I'm thankful for the option to turn it off.