It's not the first time Sega has tried something like this.
Phantasy Star 3 had a system where the battle theme would change depending on whether you were
winning,
losing, or if it was
currently a toss-up. So it's interesting to hear that Sega revisited this concept in a much more fleshed-out capacity. I hear a lot of good things about Skies of Arcadia, so I might check it out some day.
While I'm on the subject of
Phantasy Star 3 and cool things it does with music, it also had the really cool idea of having the overworld theme gain more instruments and grow in complexity as you recruited more party-members, so when you're all by yourself it sounds
very barebones. Gain a second party member, and
the melody becomes a duet. Gain a third,
there's now an additional melody in that background. Gain a fourth,
yet another melody. Gain your fifth and final member, and
they'd finally layer on the percussion to make it sound like you're truly on an epic adventure.