Cool game, and neat AI behaviour. There are two things that I'd lack to mention, though:
The tutorial, try to always put it in-game. Even if it's just a image of the controls layout for this type of game. Do not neglect tutorials or "how to play" inside the game. You can check the site, yeah, but that's not the point.
The other thing i'd like to mention is that you do have a Quit game button, but only in the endgame screen, in the main menu there's not a Quit button.
Cheers, i hope this helps ;)