ok i have a bunch of ideas.
first, they should have a small quantity of space buildings/units, none of which could like attack in a cheap way, but maybe more of a science vessel type thing, and also some kind of spy sattelite.
terran:
-Im a big fan of nukes, and this is an idea i have had for a long time. they need to have an orbital weapons platform(space unit) that uses mana to power a powerful laser area of effect attack. it would be targeted by the ghost, and would cause a line of lasers to rain from the sky and attack bases/units. it would function similarly to a nuke in that the ghost must target it for a few seconds first.
-i like the idea that someone threw out of having male and female marines, and just make it random when u press the build marine button that either a male or female pops out, but they have the same attack abilities just different models.
-the other idea someone said about trenches would be great too, but they need to make it like this: any ground units on foot can dig a trench, but it takes time. you get to choose the size of the trench, and when it is completed you can place small ground units into it. it would then be covered by fog of war to enemies, unless they fly over it with air units or come close to it. The trench would also make the % of misses high, but should multiply splash damage that is affecting the area(think about it, if you are standing next to a guy that gets blown up and ur in a trench, its gonna hurt more)
zerg:
-tunneling units. thats a must. it would add such an element of strategy to the game. what they need is to make it so like only zerglings and hydras can tunnel, and you must research to be able to build special lings and hydras with the ability that take up extra supply. and there needs to be some kind of limit, like if you burrow underwater u die, and you cant go thru steel walls or whatever.
-ability to infest units and take control of them. kind of like banshees in wc3, or mind control, you can build a special unit that will automatically go to an enemy unit and jump on it and take it over.
my god i cant remember the other units, but i had some cool ideas before
they need xel naga too, and they should be VERY powerful. but they like take a long time to build with or something. they should also have certain buildings that they could make that could like take control of a number of zerg units, or disrupt their activities(slow mining etc) until they are destroyed. the xel naga created and controlled them, so this should show through.
arghs i cant remember my stuff........ill post stuff as it returns to me.