Hey, I played your game. I'm a fan of VVVVV, and was a little surprised that I couldn't switch gravity in the middle of the air, but I think for this style of game, what you have makes sense.
For feedback, I think the player falling speed felt fine.
Regarding difficulty, I think you can have it ramp up a little faster. Once you get a feeling for the game, it doesn't get that interesting until it gets fast, which takes a few minutes. Getting to that point more quickly would be good I think. You could also do things where it gets really difficult for a stretch of 10 to 15 seconds, and then gets easier so the player gets a breather, then ramps up again.
Another thought I had was the sprite for the main character doesn't really match the simple vector graphics of the level. It might make sense to have a more monochrome main character? Just a thought, and you might already be thinking about replacing them, but figured I'd mention it.
Anyway, fun game!