It's a good game, I liked it. It would've been better if there had been some sort of explanation regarding abilities, but it's nothing terrible.
However, I believe that the lack of challenge is indeed a problem: I never felt I was in danger or could've lost a fight. I also didn't like the fact that there wasn't anything like a proper ending. A cutscene or just a couple of pictures a la comic (or even only one!) as a way of telling how this ended would've been nice. It felt incomplete otherwise.
Still good, nonetheless.