I'll now complain about Empire At War.
Rebel Artillery. Their rockets are friggin' powerful, the rockes home in, they can crush infantry and scout speeders under their threads and they also naturally have a long range. Also, most of the time you'll notice them after they've fired a rocket barrage at you, when it's ofcourse too late to move your unit out of the way. AI also likes to spam these units. For some weird reason, Empire doesn't use their artillery at all.
Also, Rebel Torpedo Frigates in the expansion. They're so fast and small that turbo lasers can't hit them, they can outrun missiles and torpedoes most of the time and normal lasers hardly harm them. Fighters, bombers, capital ships and everything else have hard time attacking them because of their speed. Also, the ships have laser guns (anti-fighter) and a special ability to deploy cluster bombs (also anti-fighter thing, except way more powerful). Is it weak? Well, it's armour is. But the shields, the friggin' shields! Oh, you almost got the shields down? Oh look, now it runs away and will soon come back with full shields, like nothing had just happened! Also, tractor beam just slows it slightly! You need two tractor beams to actually slow one down. Does AI like to spam these units? Sure as hell does! I had battles where Rebels had more Torpedo Frigates than fighter groups! They just keep on coming! Wave after wave after wave! It's like Rebels got their military doctrine from Soviet Union!
The best way to destroy those hellspawns is to use the Death Star. You can't outrun the superlaser, bitches!
SW: Empire At War: Forces of Corruption? More like, Forces of Frustration!