I agree with most of the other comments. The puzzle mechanics are really nice, although I get the feeling that they could be expanded upon a lot more -- there are thirty levels in the game but it almost felt like there was more tutorial than actual challenge (counting the levels after 26 as tutorial). Graphics are nice although some sort of a face would probably have made it a bit better and music was a plus.
Level 26 was pretty evil if it's supposed to be finished the way I did it, and probably how davidpuralocura did. I'm not saying that's a bad thing, but it's sure to make some people rage. And 19 can be passed either with a "correct" looking approach or an approach that looks like it should be a fail but takes you to the next level (moves for the failwin approach are DR UL UR DR UR UR UR).
I agree with ercjaeb that I think it'd be nice if we could see where the exit will appear, and ideally also things that make effects unambiguous like where platforms will appear if you walk on a platform that makes them appear, and where teleporters will take you. And if we could see the entire map without moving the character around. But those are small nitpicks.
I didn't have any issues with using arrow keys to control diagonal movement and thought it seemed pretty natural. This might be a case where most people think it's just fine and don't bother to comment about it, while people who it's an issue for are going to comment about it.
And I need to go wash my brain after reading that comment by Thefemaledude, especially with that username.