I personally don't like two things about this game:
1. When pausing the game there is only an option to retry that particular room. I'd would be neat if there was also an option to retry the entire level, so you don't need to go trough all those menu's.
2. It doesn't have a little bar, like most games have, that tells you what level you're playing. This would be useful, because you can more easily remember when a difficult level is coming up.
The "story" doesn't affect the gameplay much, but it is weird. It makes very little sense. The bird stealing the treasures feels a bit pointless. I was expecting there to be a boss-level where you had to steal the treasures back, but there wasn't. I'm basically clueless as to why this stuff with the bird is in the game. The fact that Duke can instantly leave after finishing a building is also just stupid, as some levels wouldn't even be possible in reverse. It would have been more logical if Duke was somehow trapped in the building by some sadistic wizard creature. That way the story would have made more sense. But the story as it is now is not really annoying, it's only just weird; it doesn't stop the game from being fabulous.
I'm also a little disappointed that there wasn't a boss battle. But that's just my own fault I guess, because I shouldn't really be expecting there to be a boss if there aren't even any living enemies in this game. But I would have liked seeing a boss with these gameplay mechanics. I imagine some beast -that bird for example- chasing you trough different rooms or something like that.
What I like about this game is that it's quite unique even though it's a platformer. It also has quite a lot of levels. Similar games like this that are posted on Newgrounds only ever have 20 levels or so, but this one has 120, which I find impressive.