Besides the fact the game is just great, the mutliplayer is friggen awesome.

It's basically a war, you fight (after you pick one of the 3 sides if i remember correctly) to control sections of the land, and you get updates of what's going on, and which squad (mini clan) is doing the best. For example while you're looking at the battlefield, it will flash saying Emergency, Blah is under attack, all Tarkians report to this sector and defend it. Then you and your squad goes there and you have to fend off opposing players etc.

Squads can earn cash to buy new parts for the mechs, also squads can partake in a lottery which will give a special part to a person everyone now and then obviously providing they win. Plus the community is pretty mature (considering it's a mech sim).

All around this game kicks ass!