Ooo it's definitely worth giving it a proper go. I even got one of my non-indie-game playing friends to complete it... twice!
I think it's a great example of replay value in a game. Normally you would play through the game killing everything, but it can also be played without killing anyone. You unlock/upgrade different abilities, allowing you to play in different ways. There's a variety of weapons. The levels are complex and have secret areas. There's a lot of story to read and it subtly changes based on your actions.