Eh, I've just been thinking, and I've come up with a few suggestions:
First, a few new human weapons, to smooth out the choices and offer just more options (don't have numbers since I'd be bad with damage/reload/etc. numbers, either overpowering or underpowering something):
Grenade launcher, S3, very (slightly longer then md/shotgun?) slow reload, low ammo (one shot per "clip", only a few clips), between 500-700 credits, shoots in an arc, does a lot of damage, wide blast. More damage then a lucifer, much slower reload, much harder to aim. Faster projectile though, although it should bounce around and explode slightly (a few seconds) after it lands. Should make a noticeable sound so that aliens will have a chance to escape. Noticeable kickback. Specifically meant to be used against things like Tyrants and goons, since it should be able to shoot, and explode before they can completely escape, but Dretches and other faster moving aliens should be able to escape.
Submachine guns (machine pistol, etc., should probably be displayed as a pair of weapons), S2, 100-300 credits (could be made free if it was about as powerful as a rifle, just different). Not as accurate (more spread) or as long range as the rifle, but faster rate of fire and 1.5x the clip size (45 shots per clip). Twice the reload time. Should be more effective at close quarters then a rifle, but not as effective at longer ranges and . Sort of a cross between the chaingun and the rifle. Not loads of kickback, should offer a good weapon against the smaller, fast aliens at closer quarters, although rifle would still be better against the small dretch (since it is more accurate). Dispersal of fire should be so that it disperses into about the amount of area that a mara takes up.
Various more expensive ammunition for the firearms would be nice (exploding bullets, etc.), although not for the chaingun for balance purposes

*thinks of a chaingun with explosive rounds and drools* This would give them more worth later on in the game, when the matches are ruled by lucis, pulses, flamers and chainguns. Cost should be comparable with the damage increase.
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Of course, in return, the aliens should get something, so:
I propose that dretches, basalisks, and adv. basalisks be given a dart attack, which does very low damage, meant to be used to knock jettards out of the sky. They'd get one shot (with reloads available at a booster so that they actually have to visit their base again for once) and it would be pretty accurate, but not a viable long range and effective weapon against fleeing/strafing humans. Probably should be effected by gravity, but not in a parabolic manner. Should NOT communicate poison.
I'd also like to see a single long ranged class that could be used against human bases, but which is defenseless at short range, but I'm not sure how that would be balanced in (at all, although the aliens have a need for this the aliens are predominantly short ranged, so it shouldn't give them something that can be their new, long ranged tyrant, but it should be more usable as a long range then the adv. goons).
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More starting classes for both aliens and humans (which would, of course, do different things) would be cool if it could be easily done, although again, I'm not sure how that would fit in.