Although my computer has had difficulty running Unity games in the past, I can run Chivalry Medieval Warfare at a reasonable fps. Attempting to run this game, it is at a maximum of 2-4 FPS and there is constant clipping - the darkness appears to be thousands of disconnected polygons flying everywhere, obstructing my vision - even in the main menu. At times, I see nothing at all (again, in the main menu where you're supposed to be seeing a lighted raft).
I expect that this game is using some graphics card feature that is not supported by those of us with problems in this thread. (My graphics card is "AMD Radeon HD 7400M Series").
Note that, in my case, if I go into a game and look straight down, I get 30+ fps. If I look back up, the crazy sky drops the FPS back down. Lowering the resolution to 800x600 helps - I can look at the crazy sky and get an fps of up to 8.
Here are two screenshots of this "clipping"/"crazy sky":