This DLC would have been really great if more people had bought it, since multiplayer chance to play Dreadnought maps depend solely if other players have gotten it as well.

Joining the one game I ever had a chance to play any Dreadnought content, you basically get a chance to to control a DN to fight with during battle. It packs a lot of firepower and moves slowly, but you'll be having a blast if you get one of these. Unfortunately, I would have to say steer clear from any of the map-based DLCs because with the WH40k Space Marine MP community dying off and THQ/Relic not updating this game anymore, you're better off setting your sights on Dark Millennium instead.