Well how exactly can I describe it's gameplay? You make 100's of units, send them at your opponent, they shoot projectiles at each other. You make 100's of bombers, and destroy your enemies defensive structures with them. You make 100's of anti-air turrets to shoot down enemy bombers that are trying to kill your precious big guns that can fire all the way across the map. You make 100's of structures to produce energy, metal, and convert energy into metal. Strategy involves lots of scouting, unit choice, and also you can heavily micro your units to get more out of them (mostly with air units). After big fights there will be a huge graveyard of metal that you can slurp up (reclaim) to make more units with (perpetual metal!). Your commander unit can turn invisible, and has a weapon with short range that instantly kills anything (called the D-Gun). So he's really good at countering early rushes, even though rushing is still really effective because metal extractors and windmills die in like 4 shots...
Just imagine epic futuristic combat and this game delivers on all fronts. There's ships, seaplanes (that land underwater) hovercraft, tanks that go underwater, K-bots (mech warriors) that transform into boats, construction aircraft (ever wanted a flying peon?). THIS GAME HAS EVERYTHING! Radar, Sonar, Nukes, Popup cannons (that can survive nukes), Anti-missile defense systems. The list goes on and on and on and on and on and on and on.... and on....
List of problems:
Pathing system isn't very good (the more units on the map, the more the pathing system is dumbed down even though modern computers can handle it without sweating a drop)
Not balanced too well. The Arm are in most cases better than the Core, and some units are strictly worthless (even though there's 150 to choose from so no wonder). Honestly though it doesn't matter too much since the units that are used the most for each faction are fairly balanced (although I'd still give the edge to Arm).
The races are very similar to each other. It's like Warcraft 2, where there are only a few differences on each unit, but with 150+ units, again it doesn't really matter.