Well basically the single player is more of a RPG than RTS. You select up to 4 squads of varying units (only space marines are playable) which you play with through the stage. You still capture points throughout the stage, but their significance is to replenish 'fallen brothers' from the squads you started with. Typically, you face a boss at the end of each level, which is like a supercharged hero from the other factions...
I am a loot ho, so I really enjoy picking up all the randomly dropped wargear and kitting my guys out for the next mission
The multiplayer is more Role Playing Strategy.... not an rpg or rts per se. Basically, still no base building again (just your const yard equivalent and one turret), but you can now build units, up to your unit cap....