This game is firmly in the "work of art" game category. It's all about the atmosphere, the sense of scale, the space, and these things it does amazingly well. Yes it's just a series of "go to where boss is, kill boss, repeat". That's fine, this is not a hack-and-slasher, it's a highly innovative puzzle game that transports you to a completely alien universe that is somehow quite familiar.
Where it loses a star for me is the camera controls. OMG seriously. Double the time taken to kill colossi because of that damned camera with a mind of its own.
FYI you don't have to steer the horse. Point it in the direction you want it to go, press and hold triangle, you'll get there with no left stick required 95% of the time.