What a treat.
I don't know what I was expecting going into this, but I was pleasantly surprised. Supergiant Games managed to develop a game with an interesting premise and story, rounded out with solid gameplay mechanics. The narration is inventive and interesting and relevant, though not without flaws. There were a few moments when I thought to myself, "what the fuck he is talking about again?" But those moments were fairly rare. And the music was fantastic. And not really what you'd expect from a fantasy game.
The artstyle is beautiful and the level construction, while almost entirely linear, manages to make the game feel remarkably less so. They kept adding in weapons and power-ups as you go to keep the gameplay fresh throughout the entire 5 or 6 hours of campaign. Sometimes I felt like the shop items and upgrade system could have been better fleshed out with more options, but this is a minor complaint. The ending is satisfying and provides a moral dilemma that actually made me pause and think about which path to choose. It's all a very nice little package that's almost as good as World of Goo and Braid (if not as good) and it's certainly a good sign of things to come from the developer. Buy it.