I'd suggest that you freeze the player's movement for a bit inbetween transitions so the player don't accidentally die. Especially in rooms where the player is really close to a gap in the next room.
Some of the hazards isn't very clearly communicated that they are hazards. Like the lava for instance. It looks like you can walk on the ground above it,
Keep making platformers, there are a lot to learn from them. I'd suggest you playtest your games more with friends and even people that don't play games much. Just to see how they play. You'll learn so much by doing this!
Good job tho, please keep making stuff!