Franklin from MMORPG had the possibility to play 3v3 demo match at Pax Prime and is talking about it in his preview.
Combat is fully action-based so not tab and 1, 2, 3. You must aim and hit your target. So more like an FPS game which is good. Weapons are kicking when fired or when you get hit. So you must count with friendly fire and be careful what you are shooting at.
He played only 3v3 which will help mostly to test the core mechanics but the final game will be of course much more with bigger fights, maps and so on. And it could be even 1000 marines on the battlefield.
Even the game development is in its early stages the combat feels solid and is promissing. Let's hope the development will go the right direction until the final release.