acare84: It is a standalone expansion. You can play all races in single player, but you can only play as two races on multiplayer.
Yeah all the expansions are like that, semi-standalone which I suppose is a stand-near.
Soulstorm is pretty crap though, it felt very lazy but then I thought that about the dark eldar & sisters of battle as well so I suppose it's ftting.
In fairness there are a few good elements, stuff like convoy interdiction to prevent the enemy building super weapons but it still feels like a skirmish game with triggers. Dark Crusade could get away with that (a bit) because it was a bit new & introduced stuff like the wargear & the risk style global map
You might like it though, thats what demos are for.
Is the beta download just a linked EXE or an actual steam install?