For starters, this game's atmosphere is outstanding. It kept me on edge and really captures the dark and gritty nature of the game. The story is great; it's an interesting take on the dispute between God and Satan. And the art is great. This is definitely one of the best-looking flixel games I've played.
This game's only fault is the gameplay. Don't get me wrong, the controls are smooth and there isn't anything wrong with them, but to me the game itself didn't feel all that fun, or at least not enough for me to do another playthrough. This is something where it's main driving force is its story, which can be interesting, but more often than not that feeling fades after one playthrough, even with multiple endings.
This game certainly has its merits -- a great atmosphere, compelling story, and multiple endings -- however those merits aren't enough to bring me back a second time.