Looks like a decent idea. Do you have plans yet for what the end goal will be, besides repulsion of the invasion force? I mean, that seems a little shallow for a semi-RPG like this.

It actually isn't repulsion of the invasion force, instead the players are part of the invading force. Essentially I wanted to make a fun and simple map similar to SC1's "Normandy Invasion" except using the resources of SC2's data editor and not involving Wold War 2 or Nazis. So the goal, in the case, is to successfully invade the city and take it over.

Right now I'm still planning a lot of this, too. Though it will ultimately just be a form of a hack 'n' slash RPG, I at least want the abilities and whatnot to be interesting enough for people to want to play it. I remember playing Normandy Invasion for hours and hours when you literally just upgrade armor and weapons and kill waves of enemy units, and somehow that wasn't boring. My hope is I can achieve that with this, though I wont know until I actually get the data editor stuff in there.

If anyone has suggestions for some simple and realistic abilities for some hero mercenary units or new heroes entirely, feel free to suggest them. The only things I have planned as far as that goes are:
Mech Operative's Seeker Missiles (starting with only 1 fired and at maximum level, 3 total are fired at nearby enemies).
Mech Operative's Shock Pulse (emitting a small AoE shockwave around the hero, doing more damage based on the ability's level).
Mech Operative's Missile Barrage (starting with 2 fired at an area and 8 at maximum level).
Med Tactician's Life Leech (stealing life from an enemy to heal itself and nearby units).
Infantry Commander's Grenade (simple grenade that can have various upgrades to add effects to the blast, like resonating damage in an area or stuns).
Covert Operative's Turret System (starting with 1 turret and at maximum level can drop 4 total, and can learn various types of turrets to drop).

I'm trying to stay away from any sort of psionics or Protoss units, but I have a feeling I'll end up putting a caster in anyway along with a DT.

I've always wanted a Normandy map for SCII, it'd be so epic. Normandy was probably one of my favourite maps of all time from SC, so much replayability and it was so fun. Though I do agree, World War II has grown tiring, but everyone loves killing Nazis, they're the ultimate bad guy!

Ah, didn't read the Plot carefully enough. That does open up more possibilities, though.

I have an idea relating to the Medical Tactician.

Oh cool, great idea. Adding that as the customizable ability for the Medic.

Oh and if it isn't already assumed, any ideas I use will be credited in the final release.

Add generators that you have to defend, and then a core that you need to defend if all the generators fall.

This isn't a PvP map, it's a player versus computer map. If there was something necessary for the players to defend, then I'd totally do something like that.

Oh, I read it wrong then. Whoops.

Update!
Half of the terrain is now complete. I decided to add 2 more units, an Assault Commander and a Psionic Tactician. I was trying to avoid magic-users in this, but I think ultimately it would be more fun to have one or two. Also, I'm making this a 6-player co-op rather than 4-player.

I also added new abilities:
Covert Op - Sniper Round: Shoots all enemies in a line with a single bullet.

Medical Tactician - Healing Aura: Heals surrounding units, and gives himself an attack speed buff.
Medical Tactician - Energy Shield: Protects the target with a shield of energy that absorbs damage, and deals minor damage to attackers.

Assault Commander - Rocket Leap: Flies the unit to a target area, dealing splash damage around the landing point.
Assault Commander - Assault Rally: Calls down assault troops to a target area to help kill enemy units. Leveling this ability calls down stronger troops and probably more of them.

Psionic Tactician - Energy Bolt: Shoots a bolt of energy at a target, dealing minor splash damage upon hit.
Psionic Tactician - Charge: Charges an enemy, producing a short stun effect around the target.
Psionic Tactician - Clone: Teleports to a target area, leaving a hallucinated clone in the caster's place. The hallucination taunts nearby enemies, but doesn't have much survivability. Leveling this ability increases the hallucination's health and increases the range of the teleport.
Psionic Tactician - Psionic Storm: Calls down a storm on the target area. This ability can be upgraded to include various effects on the target area, like leaving a resonating damage debuff, lowering speeds, etc.

I like how you can personalize Psionic Storm ability!

Yeah, I figured that would be a cool feature.

I added 6 more screenshots of the terrain. I'm thinking of extending it north a bit so there are 4 distinct areas players have to go through, rather than 3.

I'm starting to finally add the abilities in a level-up fashion, but haven't done more than the Infantry Commander yet. Ultimately you can level each of the 5 abilities up to a maximum of 5 times (though at 20 levels, you can't get 5 points in each). The 6th ability (the mercenary's tech specialization) increases in power automatically with the mercenary's level, but specific upgrades and variations need to be purchased with credits that will be earned through the course of the game. Using the tech spec ability will simply be a matter of hitting the hotkey for it to bring up a separate ability submenu full of variations. For example if you want to place a normal Turret as a Covert Operative, you would hit the space bar to bring up the submenu full of Turret variations, and choose which one you want to place by hitting the appropriate hotkey (Q, W, E, R, T) or button.

Last time I wanted to use the Space Bar as a hotkey, it wouldn't work. Just wanted to let you know.

Eh, that was just an example. I have Q, W, E, R, T as my main 5 abilities, so I suppose I could use F or G as the key that brings up the submenu.

Why aren't people opting for more ergonomic-friendly hotkey positions such as A, E, R, G ? My hand feels so much more comfortable on this kind of hotkey set-up...

Because a lot of people got used to how LoL or DotA does it. If I was doing a WASD system, my movement keys would be ESDF and the abilities would be WAZXCVGTR (like they are in my Demonic map), but for this one I kept it as click-moving.

Covert Operative ideas:

I'm getting very interested.

Is there any way for me to help test?

One wisdom i can depart right away, from my experience playing Zerg Hunter RPG... is that. .don't make leveling up one spell overly important and don't make it so that new spells are useless unless you spend enough levels in it.

For the first part, to clarify, don't make the spell worthless at the start.
For second part... the same.. don't make the new spell worthless unless I put more points into it.

Quote from ImagoDeo

Covert Operative ideas:

Phase Shift: Briefly shifts the Covert Operative into a different plane of existence, making him untargetable and invisible. He can move through structures and other units while phase-shifted. Phase-shifting drains energy as long as it is active and will fade if the Covert Operative runs out of energy. If the Covert Operative runs out of energy to sustain phase-shifting while inside a structure or other unit, phase-shifting will begin to drain health until the Covert Operative is free of any structure or unit and can rephase into the current plane of existence safely.

Tracker: Melee-range ability. Sticks a tracker to the target unit, ally or enemy. That unit then appears on the Covert Operative's minimap no matter where it goes. The tracker lasts forever or until the enemy unit enters the range of an allied detector, in which case the buff will become visible and can be clicked to be removed. (Click-response behavior, in case you've never used them before.)

Injection: Melee-range ability. Injects the target with a variety of things, upgradeable and/or random. Viruses? Debuffs? DOTs? You pick. Or let the player pick.

Phase Shift is a cool idea (essentially seems like Cloaking) but I was trying to avoid all non-detectable invisibility because of how easy it would be to exploit. If a player can cloak and run to the end to damage the one building you need to kill to win, that doesn't seem very fun. I'll definitely keep this in mind, though.

I do like Tracker, but that also required this to be a PvP map, which it isn't.

Injection is awesome for that Tech Spec idea. I can give the Turret System to the Assault Commander (since he doesn't have one) and use Injection for the Covert Op.

Quote from UnholyUrine

I'm getting very interested.

Is there any way for me to help test?

One wisdom i can depart right away, from my experience playing Zerg Hunter RPG... is that. .don't make leveling up one spell overly important and don't make it so that new spells are useless unless you spend enough levels in it.

For the first part, to clarify, don't make the spell worthless at the start.
For second part... the same.. don't make the new spell worthless unless I put more points into it.

Since this is a Player versus AI map, there wont need to be much testing until I publish it for everyone to test. A majority of this map is in the Data Editor, and as long as I can get all the abilities to work while playing it alone, they will work for other players as well.

As for spells, each ability will have a maximum of 5 levels. Obviously each spell is more powerful once leveled up, but they each should have their own uses. For example the Mech Operative can fire Seeker Missiles at an area that will do AoE damage to units but he can also fire a Missile Barrage on the units for a similar effect. The difference will be that Seeker Missiles might do more damage to infantry units whereas Missile Barrage will be more effective against heavy armored enemies and buildings. Levelling Missile Barrage may be more effective, ultimately, but you do have to deal with more lightly armored infantry units than vehicles. I'm also trying to make each ability unique from the others so that there aren't too many similarities. The Medical Tactician can leech life from an enemy to heal himself and a small area around him, or he can pop his healing aura and heal everyone around him while buffing himself. The leech will do more damage than any speed buff, but he heals less units. Those are the sort of trade-offs I want to accomplish.

I just had a brainstorm. To make Injection AoE, you could have a simple needle-grenade system - that is, a grenade that explodes and actually fires missiles in all directions. It might be a pain to code, but it could work.

Also, the Mech Operative's tech specialization could be mech type. There are a lot of terran units that would work besides the Viking - predators spring to mind; or scaled-down thors/odins; even siege tanks/breakers would be good, unless you're using them for something else. Hellions and vultures don't work quite so well. Goliaths are good. It's all up to you, of course - just throwing ideas out here.