Just played a pretty epic skirmish against the hard AI (defaults to normal). Took me about 15 minutes to win, ended up with three bases to his paltry one. Final rush was three Spartans upgraded with Spartan Lasers, five fully upgraded Warthogs, and six of the UNSC uber units (game calls them that, not me...think they're called Vultures?) fully upgraded with the 2x Bombardment upgrade. He came at me with two Scarabs, the Prophet of Regret, and a bunch of honor guards. One MAC Blast and two bombardments later, his entire army was gone, and his base lasted about fifteen more seconds. Oddly enough, the framerate held up the whole time.
Loving this game the more I play.