Really nice idea and execution! The core mechanic reminded me of my own game (/shameless self-promotion:p), although you had a different take on it. The health loss on leaving the horse's aura had me worried for a second, but then I realized the health is replenished when you return to your horse, which made it very forgiving and more of a puzzle. Also appreciated the show-don't-tell approach to teaching the player how the game worked, instead of lengthy written instructions.
Oh, and of course, the graphics looked really good :).