i personally think the heavy distortion on the guitars and the overall hard rock sound right from pretty much the start don't go all that well with the theme.
my first impulse really is that this level of intensity would work better at a later point in the arrangement, to top it off and raise it to another level. it all sounds quite good, make no mistake, but i think it's too much, too early, for this theme.
i like the dynamic arrangement. it's quite lively. a lot of good stuff here. but i'd really prefer a more gradual buildup as sonic intensity (and distortion) goes, for this theme.
i think 0:17+ could hit really hard somewhere in the 2:00+ area if you prefaced it with an earlier more acoustic, or just less distorted, version.
the 15 sec intro is great, btw. but the field theme in full metal armor right after that.....it's over the top in a way that's thematically jarring, to me.
maybe listen to some Gentle Giant or something for inspiration...to get some additional ideas on how to transmogrify the main theme without fully metallizing it right away.
well, just an idea.