Probably the best 40k gaming experience as a whole out there. The RTS controls are somewhat outdated, given that it came out in 2008, but the core of the game is pure 40k in all the best ways.

Be sure to download the Unification Mod to greatly expand the amount of Factions you can play with/against. It also enhances all the models and adds new units with their own sounds. My fav new faction is the Inquisition. You can change how the campaign works by using the campaign editor. I highly recommend turning on Persistent Bases, and not using Advanced AI Tactic unless you're a masochist.