Level 29 and 39 really were the most difficult! Had the red alien that just wouldn't die from explosions on 29 - but kept trying and it finally did - and the jump to get the bomb on 39... seems the easiest way was just to pop the top box first, and then double jump off the one below it to get up. Exploit the physics a bit on the edge to jump before you're really there.
Twas a fun game, varied levels, nice combination of action/puzzle, though physics could've been a bit more polished. Cool to see the intro figure in his own role too!