All have the standard tiered units, but the progression through the respective tech trees is different for each faction.
Each has their own accompanying backstory, but more importantly each has a unique playstyle.
The first thing to mention is the three playable factions: the US Army, the Chimera, and the Cartel. Act of Aggression by Eugen Systems, the same team behind the Wargame series as well as Act of War, aims to reclaim the glory days of real-time strategy by breathing new life into the classic genre however, AoA captures that old spirit a little too well. Of course, StarCraft is still running strong, but no new RTS games have made any significant appearance lately. Real-time strategy games seemed to have fallen to the wayside amidst a slew of flashy RPGs or champion based MOBAs.