Pretty good little game here. A few of the Lost Levels certainly had some challenge to them. The one where you're the big ghost chasing the plumber on the skateboard-like thing could use a bit better spacing. It became more of a case of waiting for the random generation to work out in my favor than anything else.
Also, the "kill plumber 100 times" achievement seems a bit much. I found myself sitting here after everything else was done (all achievements, etc.), just playing through the second level since that looks like the fastest kill.
Oh, and the replay button (rarely) would stop working. The other buttons worked, just not the replay level button.
Overall, though, I enjoyed the concept and the execution was pretty decent. I'd like to see more levels using the Whomp-like creatures as those were the most fun for me.