These are by no means expectations, but these are some things I hope you look at and maybe one of these will inspire an idea of your own. 
These are all concepts of the possibilities that you could implement in unvanquished. Obviously some are more realistic than others. The names are just randomly given based on what I could think of XD
Aliens:
Dretch:
Right Click feature: When close to a corner (i.e. ceiling, wall, a pipe. etc) the limbs of the dretch and the body will hunker as close as possible to the corner. (This would require something i'm unsure the engine could handle? o_o)
Granger:
Able to charge its spit long enough to generate a nade like gobble of goo that will bounce (decreasingly each bounce, like a nade) before exploding. The splash will give increased slowness based on how close they are, but it deals less damage (more of a utility thing for the poor little guys)
Glider:
This creature is able to glide fair distances, gaining speed as it is gliding in the air (fairly long distance to make up for it being fairly immobile on the ground)
Left Click: Lashes its tail (zomgz it has a long tail 
), injecting a poison that causes slight disorientation. This is more of a defense mechanism than one used for fighting.
Right Click: Spreads its wings and sends forth a lot of poisonous projectiles, damaging anything it hits and slows them. It is able to lift off for a short period of time by charging its right click again and releasing to lift into the air and glide to safety.
Pros: Fairly good crowd control, and slightly more mobile than the basilisk.
Cons: Not mobile on ground, isn't much of a fighter by nature. (Unlike that beast of a basilisk. Basilisk don't care, he crazy.)
Bastiodon:
Okay I know that's a pokemon name, I just couldn't think of anything more appropriate.
Obviously the shaping would be different, but the idea is still the same. It's able to soak a lot of damage.
Pros: Good for defending base slightly (better than tyrants, for example. They die from 2 lucis, this guy will soak up a fair amount more.)
Good for crowd displacement (i.e. knocking apart blobs of human lead walls)
Cons: Extremely slow. It's like watching a turtle on downs that has two broken legs and a granger riding on it. Pretty predictable.
Left Click: If you thought he was tough to kill before, wait until he hunches down and prepares himself for the onslaught. Suddenly those bullets are bouncing off a lot more than before (Damage reduction, what what)
Right Click: You can hear the bastiodon suck in a lot of air, and this is a bad thing. Because shit it about to break loose when its powerful legs launches it straight forward. If you're in the path of it when it does this, you're pretty much a pancake. If you think the goon pounce was painful, this is like a roundhouse kick to the kidney stone you are trying to pass through.
Cuddles:
This little guy struts his stuff because when he's hungry, he just hunkers down and launches a vine-like claw that slowly drags its victim (presuming you actually aimed well enough) towards his grinder-like mouth (images of a woodchipper are nothing compared to this). The human ensnared has limited ability to aim (similar to basilisk) and cannot move, aside from where he is being dragged. noms noms.
Pros: Great for efficiency. He can take out enemies that cost a lot more than he is worth, providing he is alone and the human isn't positioned to shoot him enough times to release the hold.
Cons: Isn't much of a fighter. He just wants a hug. :/ Humans are able to help the victim in the snare out by shooting at him, if he gets below half life the bond breaks and the human is free.
This next alien is probably the most crazy and highly unlikely idea of them all...:D But I like him all the same <3
Little Big:
This guy was the runt of the litter, and is a result of the cataclysmic event of a Granger and a Hovel spending too much time together. The cost to begin the first phase of evolution -evolving into the creature that grows into 'Little Big' is the first step in becoming the little guy- is around 9 evos.
You must be a granger, enter the Hovel, and pay the hefty price of 9 evos. Once you pay, the hovel will change shape and grow a fair amount. There will be a spikey shell-like shape with stubs (soon to be legs) and tusks protruding from the hovel.
Once that process of growing is complete, when you have 2 evos you can complete the evolution. During this time you can pay 1 evo to gain half the benefits of the full evolution (more health) but do not gain the full features (i.e. mobility, combat, right click).
Once the second phase of evolution is complete, you will turn into 'Little Big'.
Growing exponentially, you will make a Tyrant look like your bitch. You're so stupendously large, the only map for you is Karith or Transit basically. The horned shell becomes more defined (and provides some brush, even), and your tusks grow much larger. Of course during the first phase of growing it won't let you begin the evolution unless you can cover the entire area, so building the hovel in an ideal location is a must.
Left Click:
You sweep your tusks the old fashioned way, knocking everything you contact a far enough distance to make them think twice about shooting you.
Right Click:
You cover any gaps, sheltering fellow grangers. The amount of time you are able to shelter is almost enough time to rebuild the overmind.
During this time, you gain a lot of damage reduction and goons are able to snipe out towards the humans (similar to barricades in the sense that you can walk through them)
Pros: You act as a repeater for grangers to build eggies on you ^-^
You have enough health to make the Bastiodon jealous. Really jealous.
Very useful to protect forward bases (i.e. it's much harder to shoot the eggs and booster when a giant alien with nasty tusks are protecting them)
Cons: If you thought the bastiodon was slow, you might as well go make a tea while this guy lumbers to his destination.
Takes a lot of evos for little gain in map dominance
It's fairly hard to combat the humans, as they are like a swarm of bees compared to your movement.
Humans:
Battlesuit Concepts
Futuristic Upgrades:
Battlesuit Hangar:
This is where the humans will be able to enter with a battlesuit and do some fine tuning (obviously costing a lot of money)
The various upgrades would be:
-Grenade pocket upgrade (2 instead of 1)
-Armour upgrade (slightly more resistance, cost can be based on cost of light armor/helmet vs bsuit and compare them)
-More powerful medkit (heals for longer, faster. etc)
-Able to jump higher/take less fall damage
-Can upgrade HUD to include a place where there is a zoomed in part of your crosshair (not as much as MD) but can toggle heat sensing (will show aliens much better in dark places)
The Peace Maker
Instead of upgrading that old battlesuit, we have a new sheriff in town. This suit is built for combat. You will have even more limited vision but it comes with some...perks.
Left Click: Default weapon
Right Click: hold down to charge your phase shield, release to bash. The longer you hold, the more damage/further the alien goes (Depending on the size) The suit also comes with radioactivity which will harm anything within a distance of it. These guys are usually solo workers and don't work well with others.
Polymorphic Upgrades for the Battlesuit
I figured instead of always having to go to the armoury for supplies, or the battlesuit hangar, why not just use what you obtain on the battlefield.
This battlesuit method will be able to take parts from an alien (by pressing Q, so on death some aliens will have to create an invisible structure that is only available to the battlesuit) that gives them the option to upgrade.
A battlesuit may only use one of these 'upgrades' that are torn from the alien.
Dead Basilisk: May throw the basilisk on your back and it will act like a medkit for you, permanently. (much weaker than a medkit, but in the long term it is very useful)
Dretch: Can be worn as a hat. Spiffy isn't it?
Tyrant: The head is torn off and you use it as a shield. The bonus is gaining extra base health. (when I think of it now it isn't very original is it? Alien anyone? Surprised I didnt think of this until typing right now...>_>)
Weapons:
Concussor:
Knocks everything in a cone back, depending on the size of the creature. Will also deal minor damage (although a fair amount to dretches).
Pros: Good for alien dretch storms.
Cons: The bigger aliens arent very affected by it (goons+)
Phasegun:
This weapon is a mobile buildable weapon. It is similar in style of the mortar, except shoots big beams of hurt instead.
It takes a little to charge, it lasts not very long (say 3 seconds of burst), and then has a short cooldown. During this time, you cannot leave the weapon. It takes a while to load/unload as well.
Pros: Excellent for stubborn objects, and buildings.
Cons: Easy to kill by killing the person controlling the weapon.
Maybe this has sparked some imagination or something, I don't know :D
