Forgive the acronym attack for a second, this is for those interested enemies that think... Basically artificial intelligence.
Most game AI is decision based (If A, go B, If C and A go DotA). The end result feels natural (except for the Crysis AI which became terribly indecisive due to so much stuff going on, which they fixed in Warhead) but it can be exploited or predictable, particularly in an RTS, unless an obscene amount of work is put in.
There's this new RTS... thing... It's a hybrid of lots of strategy genres really, and a few completely new ideas. Part of that is a new way of coding AI, and anyone interested should really take a look.
http://arcengames.com/forums/index.php?topic=24.0