I tried this out today, and was impressed with what I saw. This game really has that "one more try" factor that keeps you coming back for more.
I think there are two reasons for this - the first is that the controls are very responsive so it very rarely feels like the fault for dying lies anywhere other than with you, and the second is the instant restarts after dying remove any barrier to retrying when you die.
And you do die a lot! This means there's a real sense of accomplishment when you finally beat a level.
The difficulty curve in the levels I've played so far seems fairly well judged (although curiously I had a lot less trouble with the first level described in-game as difficult than the levels either side of it!)
I did struggle initially to perfect jumping away from a wall. In order to do this you have to jump onto a wall, hold the direction pad towards the wall, press fire to jump, then immediately switch directions on the d-pad. Most of the times where I have felt slightly cheated is when I've pushed away from the wall a fraction before pressing jump, only to plummet to certain doom. (Though this is always tempered by the fact that this timing is fully within my control, but it is challenging to pull off consistently, especially at first)
I really loved the graphic style and the music in the game - given how many times you end up retrying a level, it would be easy for the in-game music to out stay it's welcome, but this music works well as an ambient background piece, letting you focus on the gameplay.
I'd definitely recommend trying this game, and I'm looking forward to seeing what challenges await me on later levels.