Since the servers are down and I have nothing better to do, I thought I'd start a thread about aspects of Starcraft 2 borrowed from other RTS franchises. This is not a QQ thread about how Blizzard is ripping off other companies; the purpose of this thread is to show how good the good people at Blizzard are at making good concepts work.
Currently, all of these are from the C&C series, as it is the RTS franchise I am most familiar with. I will add more stuff later.
1. Terran Banshee
Compare the SC2 Banshee to the C&C Orca. Both are fast, agile aircraft armed with powerful air-to-ground missiles. The main difference between the two is that the Orca has limited ammo; it has to return to base to reload when it runs out of missiles. Also, Orcas are not cloaked, though they do not appear on the minimap. And finally, they are only airborne while moving. When reaching their destination, they immediately land on the ground.
The closest thing the C&C series has to the Banshee is the US Air Force General's Stealth Comanche in C&C: Generals: Zero Hour. As the name suggests, they can be cloaked, and in Zero Hour, Stealth Comanches are permanently cloaked until they open fire or are detected. It is permanently airborne, and has two weapons, an anti-infantry chaingun and an anti-armor missile battery, which has a sort-of limited ammo supply. After a few seconds of attacking, the Comanche runs out of missiles, but it automatically replenishes its supply over time (slower than it can fire them). It also has a researchable Rocket Pods ability, an ability on a cooldown that resembles the missile spam of Banshees in the Starcraft 2 Alpha and is thematically similar to the Shockwave Missile Battery upgrade in the Wings of Liberty campaign.
Banshee
Orca
Stealth Comanche
2. Burrowed Movement
I remember seeing underground units first in Tiberian Sun. The game had two subterranean units: The Devil's Tongue and the subterranean APC. Their primary movement mode was underground; if ordered to move farther than a very short distance, they would burrow and move to the destination and then unburrow. Quite a cool idea, but it was executed very poorly.
First, subterranean units were INVULNERABLE while burrowed. The only way to harm them while burrowed is to use an EMP on them, which is a superweapon in the vanilla game. In the expansion, GDI had access to a mobile EMP generator, an unarmed ground unit whose sole ability was to generate a tiny EMP effect. Good luck being in the right place at the right time, as TS maps were huge.
To "balance" these two units, they couldn't be ordered to move to an area of shroud (the black thing that covers unexplored areas of maps), and they couldn't burrow or unburrow into concrete. The former becomes irrelevant once you find the enemy base, and the latter is not a threat at all due to the cost of paving your entire base to stop just one subterranean unit. It also keeps you from building other structures because you cannot build more than one building at a time and having multiple construction yards does not speed up the process.
Roach
Devil's Tongue
Detecting subterranean (and cloaked) units requires a mobile sensor array, which I will tackle below.
3. Sensor Tower
The Terran sensor tower is an awesome defensive structure that many non-Terran players call a maphack. It reveals the location of non-cloaked, non-burrowed enemy units in its massive radius, making it nigh-impossible to sneak up on a Terran player. Fortunately, sensor towers are moderately expensive and quite fragile, making it just a tiny bit easier to crack and turtling Terran.
In Tiberian Sun, GDI (and Nod in multiplayer) had access to the mobile sensor array, which is a much more powerful version of its Starcraft 2 counterpart. Like the sensor tower, it reveals the location of units you can't see, but it massive radius also provided detection. This means that in multiplayer, you will never be surprised by subterranean or cloaked units. Even if you're an absent-minded professor, EVA or CABAL will constantly nag with you "Cloaked unit detected." or "Subterranean unit detected." over and over and over again as long as the unit is within the detection radius.
Sensor Tower
Mobile Sensor Array
More to add later. Need coffee.