There are 3 available factions: Aruthas are the 'practical' race, their vehicles have a decent amount of speed, durability and firepower. Eriins are the 'intelligent' race with vehicles focusing on speed and firepower (in form of attack speed and attack range). Finally, Trasks are the 'warlike' race with vehicles having large amounts of durability and firepower, but lacking speed.
Base building boils down to: Extractor(s) (placed on certain areas for resource gathering, usually several per area), Silos (failing to spend more than what is being mined results in resource loss), Production and Turrets (pretty self-explanatory).
There is no Skirmish mode. Each faction has its own campaign, but there's little variety to mission objectives besides 'search and destroy'.
Having more or less basic gameplay, Echelon challenges with its fast pace and a rather relentless AI.