Cute game... this walking on the ceiling business reminds me of the old DOS game Crystal Caves :)

The controls are fine for me, but I'm an avid keyboarder and I've encountered this exact mechanic before. I would include an option to switch between control styles, since I think some people will be frustrated by pressing left to go right. It sounds like you already had it set up for "absolute direction" already, so if that could be toggled then I bet at least some players will prefer it. 

Some other notes that you didn't ask for :P

• The movement speed is pretty slow IMO. And, if you were going to adjust it, now would be the time since doing that later could break all your levels.
• The variable gravity thing was a little confusing. You did do a pretty good job of showing stuff in the tutorial with just animations. But I still found it odd that the gravity would change with the surface I was standing on (that is how it works right?). Maybe some additional indicator of which direction gravity is going would be helpful?
• The music is cute but a little intense. Based on the visuals (which are great) I would have expected something more relaxed.