I think that one of the biggest problems with the AI right now is how they handle your laser mines. They simply... don't react well to them. At all. In many cases, they'll either totally ignore them when they're orbiting around a planet, letting you essentially shut down an entire asteroid for free, or they'll send in a slow trickle at them from across multiple asteroids, burning through hundreds of guys. If they DO handle them well, it's usually an "accident" (they were attacking ____ and the laser mine was in the way). Not sure what can be done about this, but... yeah

Just thought I'd throw it out there. (Also, one of my complaints is that many levels feel MUCH harder based solely on "Did you get laser mine or not?" which kinda feels... lame.
also, on a related note, I feel that defense trees are rather weak. They do have a place in the game, but I rarely feel that they're good at anything but delaying a bit (forcing people to build larger armies to attack) while delaying their creator's said buildup (with the exception, again, of laser mines). But I dunno.