A list of changes for things I've noticed in playing for the past few days. Nothing huge, and some may have been suggested already so feel free to ignore/flame.
I think the turrets could stand to have a greater tracking range. It's all right that they turn slowly, but it'd probably be more fair if they could at least see across the distance of a typical base.
On a related note why not make the turrets optionally controllable? Have it so any human can walk up to one, press the Use Object button and hop on. The advantage would be a greater tracking speed and no sight distance limitation, the disadvantage would be the human would be stationary and thus vulnerable (maybe also put a delay on the use of weapons after letting go of a turret so you couldn't just hop off and run away easily). It'd also help human builders adjust the aim of their turrets before they get attacked.
Their ought to be some way of respawning as a human without /killing yourself for those instances where you need a construction kit to make an armory. Likewise I think aliens should be able to "de-evolve" into builder for the same reason, and also into the soldier class for those times when you need more mobility (like when your Big Mofo gets stuck in a part of the map). I don't know if they should be allowed to de-evolve into any of the other middle classes. I think this would be balanced since you'd lose any of your upgrades by doing this. Also there needs to be some restrictions put on the /kill command, so you can't use it to evade your build timer or enemies.
As a human builder, when your handedness is set to right it's really hard to see the build timer against the blue screen of the construction kit. Maybe make the timer text a darker blue or bright white.
I think there should be some feedback for the Big Mofo trample so you know how long to hold down secondary attack. Maybe do the same thing as with the Dragoon pounce. This isn't really vital, but it'd at least help with the learning curve. EDIT - Timbo pointed out to me the screen rolls more as you hold down secondary attack and move, I hadn't noticed this.
I can foresee the jetpack being rather lame in wide open maps where aliens would have no way of reaching a flying human. I think maybe it should require the use of fuel that quickly regenerates when not in use, allowing say 10-30 seconds of flight per recharge.
Everyone seems to complain about the Blaster, I'd just like to be able to swap it for something better. If you can afford it you should be able to carry two (good) weapons, especially given how quickly ammo can run out.
It's often faster to sell/rebuy an energy weapon to refill its ammo than to use the reactor. Maybe make the energy refill as fast or nearly as fast as the normal ammo purchase.
I'd like to see some way for aliens to regenerate health faster while in their base. Maybe have a structure that quickens the regeneration, or have the booster do it (since it already replenishes the upgraded Dragoon's spike barbs).
Random generic ideas for human inventory items: Stimpack (stop moving and apply for a health boost), Bandolier (holds more ammo for non-energy weapons).