I know music isn't my forte but if might it be best to stay away from metal/rock as a lot of people aren't into it. I don't know how many games have had a successful time with metal/rock in the soundtracks as they're usually really crap. Not saying that stuff submited to xenocide will be but we have to cater for everybody's tastes so it's probably better to use stuff that no one will mind listening to.
You're all gonna think, hah Deimos hates rock/metal but you'd be wrong
I'm a big fan of all types of music, it's just the one type that of music that has made otherwise good games sound cheesy is metal. Some recent examples would be the new Mechwarrior game on the xbox, certain driving games 'feature' metal type music. I don't know why but as game music Metal just doesn't work.
If possible can we stick with a militaristic instrumental industrial style and work from there?
For the intro, the best thing to do with it would be to wait till we've got visuals so whoever writes the intro music can score it to the visual. Same thing goes for any of the other cut-scenes and outro movies.
Entering ground battle I think would be best suited to a pre mission build up music that plays on a sense of tension. Something that says 'come on, hurry up the aliens are attacking'. Tense but not too fast.
Battlescape music I think would be best suited by an 'adaptive mix' (for those not up to speed on the term look in the other thread to the links on gamasutra). Firstly starts out with a tension building dark 'go find the bugs' which would switch to 'oh crap' music when you spot an alien and so on.
I agree that a terrorsite mission should be fast paced and high tension music, but I think that alien base music should be 'ailen'. Something that un nerves the player, soft low key stuff maybe even in a different key to the other music. Just something to really weird the player out. Make it feel like they really don't want to be there.
The one thing I see missed here is the Mars base, For that I'd reckon a variation on the alien base music would work, only more alien. We'd need two variations on that one for the above ground battle and one for the inner base music. Something that would counterpoint the game over music or the game win music.
If anyone has played Alien vs. Predator and Doom on the playstation and listened to the music in those, I think music in that sort of style would be incredible for alien bases and the Mars base.