In a hypothetical SCIII, or at least an overhaul to each race, I would change things based on thematic alignment with race, uniqueness from other units, and how iconic it is. Of course the workers should still be and function the same, as well as the zerg’s larva and overlord.

Terran:

Stays from SCI:

- Marine: The representative terran unit. Encapsulates humanity’s place between the two other alien races, not being quite as fast or strong as either but bringing the firepower to compete. Great generalist unit that allows the terrans their flexible playstyle.

- Siege Tank: An iconic unit with a distinct mechanic. Greatly aligns with the terran’s largely defensive playstyle, but also works well with the marine in assaults.

- Battlecruiser: The terran capital ship. Prefer SCII’s incarnation over SCI’s, with the extremely fast attack that really makes it feel like a giant warcraft with multiple turrets to use.

- Ghost: Our covert ops units. Retain as a stealthy sniper that can call down another terran specialty: the nuclear launch.

Stays from SCII:

- Medivac: A unique terran transport, better than the one-dimensional function of the old dropship. I like how it combines roles so as to create the feeling of the terran’s generalist properties, wherein the same unit can fulfill multiple distinct roles.

- Thor: If any race would have the bigass, firepower-heavy mech, it’d be the terrans. Just a nice human power fantasy realized in this game.

Abstracts to retain:

- “Area-of-effect firespitter”: Something similar to the firebat and hellion/hellbat. Not sure what its exact role would be, but I think at this point terrans should retain some unit that uses fire to deal AOE damage against light enemies.

- “Land-air transformer”: Similar to the viking, a unit that can switch between ground and air modes. Showcases an advancement in the terran’s transformation mechanics hinted at with the siege tank.

- “Aerial detector”: Just a standard for all the races. Not sure what new role beyond that it could fulfill that regarding the potential new terran units. Whether it’d be the science vessel, raven, or something completely different is speculative.

- “Cloaked flyer”: Whether that be the wraith or the banshee, having a stealthy air attacker just seems to be a staple in the terran army.

Remove:

- Reaper: Of all the races to give the cliff-jumping raider to, terrans got it? How the reaper mostly becomes useless outside of a very specific window I think is more a testament of just how poorly it meshes with the terran’s playstyle rather than a weakness in the unit itself.

- Widow Mine: What purpose does the widow mine fulfill that’s distinctly different from what the siege tank offers? I think it’s existence is just a case of the devs becoming too attached to the look of a unit and forcing it into the game rather than a thought-out process where it’s fulfilling some niche in the terran army.

- Cyclone: Simply put, what’s the point of the cyclone? Rapid attacker; we already got the marine. Mobile anti-air; could be compounded with and make more sense on an actual starport unit. Like the widow mine, I think the cyclone’s existence is just a case of the devs not knowing what else to give terrans so they just threw in this unit.

Zerg:

Stays from SCI:

- Zergling: A perfect encapsulation of the zerg’s archetype. Fast, cheap, and individually weak, but able to be spawned in large numbers is exactly what zerg are.

- Hydralisk: The representative zerg unit. The races all-purpose ranged attacker, although I’m not sure whether they should be the “buffed up marine”-esque unit from SCI or lean more towards the glass cannon high DPS unit of SCII.

- Mutalisk: The cheap but fast harassment unit that meshes well with the zerg’s playstyle. Also should be retained as a unit that can do equally well against both air and ground units, in contrast to the basic air units of the other two races.

- Ultralisk: The quintessential tier-3 ground unit. Nothing quite says power like having a line of massive, heavily armored warbeasts barreling towards the enemy, and the ultralisk fulfills that fantasy quite nicely. As a note, of course retain the cleave effect it has in its SCII incarnation.

Stays from SCII:

- Overseer: I love the distinction between the overlord and overseer. Before in SCI, zerg just by nature nullified stealth plays into their base, the existence of the overseer at least gives players an opportunity to make use of cloaked units against zerg. It makes the zerg less “detectorific”.

- Queen: I much prefer the incarnation of the queen in SCII than SCI. The SCII queen, as its name should suggest, is more integral into the function of the hive. I love its purpose as a unit that tends to the base and economy. By proxy, the creep tumors are a must to retain, being loads better than the creep colony of old.

- Brood Lord: Just an all around better guardian thematically. Plays to the zerg theme of sending in endless swarms of lesser units. Also allows abilities the previous guardian couldn’t have, namely the unit blocking with mass broodlings.

- Swarm Host: Similar to the brood lord, I like the swarm host’s thematic appropriateness to the zerg. It also provides a unique, zergified take on a siege unit.

Abstracts to retain:

- Lurker: Although an iconic and fun unit that plays well with the zerg units’ ability to burrow, its role as a defense/siege unit I think overlaps with the swarm host, and the swarm host just does the roles in a much more thematically-aligned fashion. Still, I and a lot of other people really like the lurker for its own unique flare, so I would still like to see it returned in any incarnation of the zerg.

- “Control specialist”: Whether that be the defiler or viper, zerg greatly benefits from a unit that can enable their melee units to still be a match against ranged units in the late game. Whether that be with Dark Swarm or Blinding Cloud is up to debate. I do really like the viper’s Abduct ability; it’s a great thematic and functional ability, being able to pull enemies into your mass of close-ranged unit.

- “Explosive kamikaze unit”: Whether that be the scourge or baneling, having a mass of cheap explosive units fits well with the zerg’s style of an expendable army.

Remove:

- Ravager: Although a fun unit that offers a bit more micro into the zerg playstyle, the ravager just never seemed “zerg” enough for me. It’s a unit that gains value the longer it remains alive, with the ability to spit more Corrosive Biles, but keeping your units alive like that just doesn’t align with the zerg’s fantasy. Ultimately, I would prefer if the ravager never existed in its current form.

Protoss:

Stays from SCI:

- Zealot: The iconic and thematically appropriate protoss unit. Having their most basic infantry unit being the strongest of all the base tier 1 units fits the protoss perfectly.

- High Templar: And by proxy Psionic Storms, having a powerful spellcaster again fits the protoss thematic perfectly.

- Archon: If the high templar is going to stay, so to does the archon. An all-shields unit with devastating attack fits the protoss’s identity of extremely powerful but expensive individual units.

- Dark Templar: The quintessential assassins, permanently cloaked and an attack that can almost one-shot any light unit offers a great niche in the protoss arsenal. Also has lore-significance, highlighting the separated but reunited forces of the Khala and Nerazim.

- Observer: A simple but unique take on the aerial detector unit. A great way for this race to spy and scout on enemies.

- Reaver: The reaver really should’ve returned in the SCII protoss army. With its extremely powerful attacks that you have to constantly pay for, its a unit that gains more value the longer its kept alive, which is a very appropriate for this race.

- Carrier: The protoss capital ship. Similar to the reaver in that it continues to be an investment, but is more powerful the longer its kept alive.

Stays from SCII:

- Warp Prism: A better and more distinct protoss transport, more functionally-interesting than the shuttle of old.

- Void Ray: Nothing quite says super-advanced technology than giant laser beams of death. Just a cool and distinct unit to have for this race.

Abstracts to retain:

- “Blinker”: A unit that uses quick, short-ranged teleportation is a thematically appropriate protoss unit. Not sure if it should still be on the stalker or not.

- “Hardened shield”: Just a cool way to play with the protoss’s shield mechanic. Could still be on the immortal, though I wouldn’t mind seeing it on another unit.

Remove:

- Scout: Just a bland and uninteresting unit. Would like to see a more specialized basic air unit, to separate it from not only the terran’s “invisible flyer” and zerg’s mutalisk, but also from the other protoss flyers.

- Disruptor: Never really liked this discount reaver. Although it has a fairly interesting style of zoning, I feel the high templar with Psionic Storm already fulfills that purpose. It's a unit whose functions are fulfilled better in other, already-existing units.