Similarities to, and Differences from the old game:
- I have heard that this game is only the Terran campaign and that you will need expansion packs to play the Protoss and Zerg campaigns. I don't know if this is true yet. However, I cannot recall the game ever offering me the option of choosing which campaign to play, and "Wings of Liberty" just does not scream "Protoss" or "Zerg" to me. I don't mind, because I overwhelmingly favor the Terran campaigns out of both specieistic chauvanism and the ideal mixture of simplicity and firepower.

However, for those who like the Protoss, there is an optional campaign-within-a-campaign featuring Zeratul's quest to do some Protoss religious bullshit,

and you get a taste of the new Protoss structures and units. You can play a stage in this, and go back to fighting Terran battles as long as you want, or play the Zeratul campaign out if you like. And the in-game explanation for this side campaign makes sense too, and it can affect your main campaign by giving you research points as well, so it's not a waste of Terran time.

The Terrans (as far as I have progressed) still have the SCV, Marine, Firebat & Medic. The Ghost also exists, though you can choose to use a variant of the Ghost that is still an invisible soldier with a powerful rifle that can target Nukes, but has different psychic powers. There is a new infantry unit (Marauder) similar to the Firebat, but which fires an anti-vehicle/structure weapon, rather than a close combat weapon. There is a light, fast scout unit with a powerful close combat attack called a Reaper, which has a jet pack that allows it to hop up and down cliffs without needing ramps. (Dawn of War players, beware! Despite superficial similarities, it is NOT akin to the Space Marine Raptors, and should not be tossed into the middle of a crowd of enemies to mix it up while the ranged units blast away from a distance - rather it is a recon/raiding unit that dies easily but still packs a punch). The old vehicles are all back as well. You have the siege tank (no need to buy the transformation upgrade either), the Goliath and the Vulture (you can buy an upgrade between stages that allows it to replenish the mines, which look better). There is also an anti-ground vehicle hovercraft (Diamondback), a dunebuggy with a flamethrower (Hellion), and maybe a big walker thing that I have not yet unlocked.

The air/space units include the Wraith (no need to buy cloaking ability), and apparently the Battlecruiser (I have not yet unlocked it, but I have fought them).

The Dropship has been replaced by an identical-looking ship called a Medevac with, I believe, two more slots for transportation, which also has the power of a Medic - it automatically heals infantry units! The Science Vessel must be unlocked by accumulating Protoss research points, and you must choose whether your force will use the Science Vessel (it seems to have the same abilities, but I choose the other option so I am not sure) or a new thing that looks like a Protoss Arbiter, called the Raven. It is a detector unit too, and deploys little temporary defensive units, like an auto-turret. The Valkyrie from the Brood War expansion is gone, and not missed. Instead there is the Viking, which can switch between air-to-air (very slow) fighter mode (two of them killed a Protoss Carrier, though dying themselves, in what I thought would be a sacrificial delaying attack) and surface-to-surface walker mode. There is also a plane called the Banshee which is basically a Terran version of the Zerg Guardian. The only difference is, it is faster, having comparable speed to other air units, and lacks range, so you can't sit outside the range of Photon Cannons and blast them at your leisure, but it probably makes for better balance.

The buildings are basically the same, but each main structure has a choice of add-ons. The tech-lab unlocks most of the structure's repetoire, while the reactor add-on allows you to build two units in you queue simulatneously (you have to pay for both, you just get them faster). So essentially, you can either have a barracks that will make every kind of infantry, or one that will only make Marines, but makes them really fast. Or a starport that makes all your ships, or one that only produces Valkyries, and so on.

The bunkers can be sold back when you don't need to defend a location anymore, and can be upgraded in the research tree and with the armory. I'm about 10 stages or so in, and my bunkers hold six slots (which is necessary because Firebats now take up 2 slots), units inside them have increased range, and there is a gun on top, that fights even if no one is inside. There are flamethrower turrets you can build that burrow underground and pop-up when enemies come in range. You can also build a mercenary HQ similar to the nuetral shops in Warcraft 3, where you can unlock certain types of units between stages and then purchase them in the game from this building. They appear instantly and are slightly bulkier-appearing versions of the standard units, with enhanced capabilities.

For the Protoss, you still have the Zealots, Dark Templar, High Templar, Archon, Observer, Scout, Carrier and probes. The Dragoon appears to have been replaced by a similar blue thing that can teleport short distances.

There is no sign of Reaver, but you get this big-ass walker unit called a Colossus that is so tall it can step up and down cliffs without using the ramps, but is vulnerable to anti-air weapons.

When fighting the Protoss, in one stage they have this thing that more or less acts like the alien ships in Independence Day - it slowly flies over the enemy location and blasts the living hell out of it. I don't know if you ever get them as the Protoss.

I don't know if you will eventually be able to combine Dark Templar to make the red, mind-control Archon. There are a bunch of other aircraft that are kind of hard to tell if they are new versions of Corsairs and Arbiters when you are playing against them, and there are little glowing round things on the ground that I don't know what they do, but they blow up real nice.

And Zeratul can teleport. And the non-Zeratul protoss are still D-bags.

Finally, regarding the Zerg, Kerrigan is back, looks hotter (and is hotter in the flashbacks to her human days too) but has the same ridiculous claw/spine things on her foot which Angelina Jolie had in Beowolf, that effectively serve as high-heels. But so what. Also, the Overmind appears to be getting a ret-con rehabilitation. As yet, there is no zerg sample campaign, so I can't attest to any changes in them. The Zerglings, Hydralisks, Mutalisks and Ultralisks are still there (the latter of which you can actually see well enough to figure out what they look like - I thought the old ones were a kind of trunk-less elephant), as well as the same old Drone worker-units, and Overlord flying detector units (this game is considerate enough to show you the circumference of the detection range for Overlords and Missile Turrets), and things that look like Scourge. There is still the creep, but it now seems generated by little purple pustules called Creep Tumors. The Nydus Canal is more of a living organism, that pops up on its own like the asteroid worm in Empire Strikes Back, and tries to bite you before spewing out the transported units. There is something that looks like the Spire for air units, and the HQ is still called a Hatchery, and has larva crawling around it. The infested humans come in different varieties now, and some of them shoot you. I don't know if any of them are suicide bombers, but there is something called a Baneling that does that. Another new feature of the zerg is that when you destroy certain structures, a bunch of little broodling-like critters comes swarming out of the burst wreckage. The sunken colonies seem to have been replaced by a snake-like think in a round base (think of the Naga base defenses in Warcraft 3) that streches out an bites intruders, and the spore colonies can now walk around. Beyond that, I don't know if the old critters are still there, but different looking (the Overlords seemed more threatening - at first I thought they were the new Devourers). There is at least one new ground unit called a Roach, which I think spits poison or acid, but I don't know for sure what it can or can't do.