The game story and locations seem good to me, there are only a few things which I find a bit irritating. The current layout is like the big bang happens more or less in the 3rd part of the game while the 4th part seems only to be some kind of finishing off the story. There might be a lack of suspense in the last part of the game.

The battle against BUUM happens rather soon, and the final fight is only against his degenerated by far less powerful form again.
For a final battle I would expect to see him tranform to BUUM after being smashed the first time, and he should quickly transform back to his frog form after BUM has been beaten as well.

This intereferes with the swamp storyline, yes, but the swamp does not feel right there anyway. For some evil villain I would expect to see the final battle at some dark and sad place, like a rotten castle which falls apart after his defeat.

A swamp level I expect earlier in the game while on the way to rescue.
this would defeat the purpose of a swamp castle, though...


Well just some input.