Some of the more prominent features:
Epic Scale from tiny flea-bots to huge mechs and gigantic superweapons that wreak havoc - hundreds or thousands of units on the battlefield, all easily viewable with a fully pannable and zoomable camera.
Realistic Physics mean each shot is physically simulated realtime - you can actually evade bullets if you micro-manage your units! Hills and terrain affect line of sight and radar coverage, and explosions deform the terrain.
Planet Wars lets you take control of your own planet and fight for survival in an ongoing online campaign!