General Challenges. Choose between 9 Generals with special abilities and play against them : One has nuke tanks with cheaper nuke silos; one has Infantry with mini guns that can swat down air units like bugs and moe down ground units; one has air power with carpet bombing by b2 bombers and air planes with laser defense systems; another one with laser defenses that devastate anything that comes by them; another with EMP patriot missiles and cheaper Ion cannons.
New units, new defenses, more balanced, more upgrades. And a lot more skirmish maps with the ability to choose from the 3 regular armies + all the new general armies. Like Air Force General, Infantry General, Super Weapon General etc...
Plus they added a MOAB upgrade to the Fuel Air Bomb for USA armies =) ! It cost 4000 though. That is just one neat upgrade out of many you'll see in this game.
You get a lot for 30 dollars, trust me. You'll love it.