Liked the game
The biggest issue was controlling. The jump was quick and some parts you purposefully made it to screw people over in speed runs. The bosses there is pretty much no point to trying to speed run on them (especially lava ones) since it's design to stop you and make it impossible to really try to beat anyone speed run time. Also jumping on edges and such can be hit and miss.
The re-playability is pretty low especially since you made levels really bad for trying to speed run it. There are some secrets and such that make you want to replay somewhat but your basically just playing the same levels and finding a new exit which really doesn't add much.
Fix the hit areas for the lava areas and the boxes. The flame should either retract completely or you need to lower the hit area because you require precise jumping otherwise with controls that isn't quite that good. There are times where I would dodge completely except I would die since the hit box on the flames are so large. The level with the boxes to avoid the flames have serious problems. Even then your running on an even platform to a box, you still push the box and need to jump on them. Also when the flame completely disappears there is a few frames where the hit box is there.
For the good, the puzzles and such are fun and its a nice plat-former, not really a puzzle. The bosses are more memory then anything though, remember where to run to and how fast to run. Before the lava levels the game was really good, only complaint would be spikes hit box was a little big. The graphics are good and the game was pretty fun up till the lava levels. I would make the bosses a little easier because as of now, the first boss is harder then the last stage before the boss in the game.