Ok, but not great.
Before people knock me for rating this badly, hear me out.
Though this is not the worst video game song I've heard for a boss, it is DEFINITELY not the best for several reasons.
1) Not much of an intro. Basically just a fade-in of a crash cymbal.
2) Very simple beat and tune. The beat is basic and constantly used. I don't have as much of a complaint on the beat because it has those more interesting quick beats every once in a while. The tune, however, is almost stock. It's simple. It's generic. The baseline sounds almost exactly like the same note repeated and going up a fifth for a second every measure's worth, either that or a broken chord going up and down continuously. I like how there are constant key changes, but still... I do have to admit though, even if it is overly simple, it does sound pretty good.
3) The loop is almost nonexistent. I hear an attempt at one, but it sounds (no offense) like there was almost no real effort at making one.
Conclusion: Though it sounds good, and has its moments, it just doesn't quite seem like something that I'd actually see in a good game. Again, it's ok, but not great.