Warhammer 40,000: Dawn of War/Planet Fall

You start with a cutscene of some Imperial Guard getting killed by Orks. Then a few squads of Space Marines drop-pod in and get rid of them, letting you start the mission.

This one is – expectedly – extremely simple. You build a basic base (you don't need much Power so one Plasma Generator is probably fine) and start following objectives, namely capturing a few Strategic Points and wiping out Ork bases. Build four Space Marine Squads, reinforce them and upgrade them with heavy bolters (this will allow you to outrange any stationary guns on Ork buildings). Advance methodically, scout/melee with your Force Commander and shoot everything up with the Marines. Have one Servitor follow behind and build Listening Posts on captured points.

There's really nothing else to it.