Not the best I've heard...
I guess it would make an OK battle theme, but needs quite a bit more work to it.
Melodies are great, and give a mighty feel to the song. I liked the one at 0:43 most. What I didn't like is what I think is a phaser that you used at around 0:15, I think it ruined the song a little. You can keep it there, just turn it down slightly. Also, the song does have a lot of 'hissing' or static, whatever it is. I don't know if that's your guitar sample or just some glitch, but it really sounds like it came out of a 64-bit RPG :P.
I personally don't like the sound of that guitar. I think that a boss theme doesn't necessarily need guitar, but choirs and saw waves work well too, so if a guitar in the song doesn't work well, you can use those. Also, piano was way too quiet, you should turn up its volume, since I can barely hear it except in some parts, which made the song sound random.
The transitions were quite rough, for example the one at 0:42-0:43. The melody was a completely different rythm and it sort of jumped out abruptly. Even the slower part of the guitar which came at 0:55 had a rough transition to it. The transition at 1:08-1:09-ish was OK, but I think you shouldn't do that many rythm changes in a boss theme, since it would distract the player as he's fighting the boss. Keep a steady rythm, I think this song would be better off like that.
The variety is quite good, I don't see why the others see it as repetitive, but the structure is pretty wierd. Try the simple structure of: Intro - Chorus - Alternate Melody 1 - Chorus - Alternate Melody 2 - Chorus (with a few changes in the background) - Alternate Melody 1 - Alternate Melody 2 - Chorus - End. Give it a try and see how it fares in the song. As for the intro, it wasn't bad, and it looped perfectly, so nothing to complain about there.
The drums are barely heard, and they don't have the best samples I've heard. You should turn them up a little (making sure they don't drown the piano) and try and find better samples (I have a rock drum kit soundfont if you'd like it, just send me a PM). Still, they were nicely varied, had good drum rolls and fit with the song, so good job ;).
It has its defects, like all other songs, namely wierd structure, constant rythm changes, quiet drums, almost non-existent piano and some strange hissing sounds in the background. Fix those, and I think this song will be more like a boss battle and less like a collection of catchy melodies.
7/10
4/5
-Review Request Club-