First planet-to-planet landing assault was a dismal failure, despite teleporting SAS and lolicyborgninjas to disable their laser turrets ahead of time. Second assault was much more massive, around twenty transports. Before I even launch the assault, my capships and corvettes are getting laser-bombed by the enemy planetary fighters. In space. While there is an exploit in the game that probably allows this(there certainly is one that allows you to move atmospheric craft through space), it's normally reasonable to assume the game's AI is usually not aware of these things, let alone blatantly exploits them.
But I digress. The landing went relatively well. I pushed through their city, leaving them with about 4 military production facilities southeast of my army's position. Then, from a very small patch of Fog-of-War southwest of my forces, with absolutely no buildings(Library of Alexandria, motherf*ckers), a massive army of tanks and infantry pops up, destroys ALL my AA missile tanks, before being ripped apart by my battered-but-still-large assault force. Then a whole shitload of space fighters, more than can possibly have fit on the carriers that launched them, begins bombing the hell out of my assault force. No AA = no defense against fighters, and they already nuked all my AA infantry. By the time I can get my space fleet over to take out the carriers and fighters, I have only one single tank left out of a force of about 100 infantry, 60 tanks, about 60 or so artillery(both field guns and heavy artillery), about 15-20 mechs. I still won, having killed all of their citizens and buildings, so that all that was left was to mop up their remaining space turrets and scattered transports, but I still think the cost was a bit much.
Empire Earth: Art of Conquest expansion, a Large Planets random map. I had SAS Commandos and Cyborg Ninjas as civ powers. There's blatant cheating AI, and then there's Empire Earth, who will automagically spawn an army if it's under attack, among other things.
I don't even remember if that tank survived.