The game was pretty good. The graphics were ok and the music was acceptable. In particular, I loved the story as well, because it gives us a more twisted, sinister, dark view of the way we play games (since we usually play games as the hero/heroine), and it's an alternative from the usual "play as the bad guy" games (because you'll end up feeling more like an antihero rather than a villain). No, in this game we're playing as the evil villain who's killing people just because.
No doubt the story could have been elaborated on, maybe at the end of every level you could talk about what the princess was going through, perhaps in the form of a diary, or maybe have a few cutscenes, especially at the start of the levels where the new types of heroes were introduced/the boss level.
Difficulty wise, it was challenging enough for me to actually have to put in effort to beat the game, especially during the boss fight, yet it wasn't impossible to finish. The ending was also quite good, and my only problem with the ending was the statement ending with an exclamation mark instead of a period, which in my opinion would have made for a more dramatic ending (or maybe it's just me running out of things to be anal about).
For those of you who have difficulties beating the boss fight, don't give up. It took me about 10 minutes to get it done, so it's definitely do-able.