I feel torn between Dark Crusade and Chaos Rising. Dark Crusade was arguably the high point of the original Dawn of War series. But then you look at Chaos Rising and see epic fights, tough choices, and...ELIPHAS! OPEN THE PORTAL!
Dark Crusade and Space marine, Dark crusade has many mods that i've downloaded. Space marine was the first 3rd person shooter i played from relic, (unsure about firewarrior though i liked that) i love the storm bolter! dawn of war 2 had a very good campaign but multiplayer felt like coh, bummer.
I'm going to be a bit cheeky and say "X-Com Enemy Unknown" I know it's not a 40k game, but if anyone's played it you will know with its squad based gameplay, different loads outs and trainable psykers it wouldn't be too hard to turn it into a fantastic 40k game. Just a reskin really. Other than that, then I would say Spacehulk really had the 41st century's grim dark atmosphere down to a tee, I enjoyed Spacemarines too, but I really do prefer rolling some dice with my friends on a 6 x 4 over any 40k video game so far.
soustorm with mod (now soulstorm mod are better also modder have fixed the soulstorm campaign defensive building and fok is coming to soulstorm) space marine chaos gate is too old: dow is old but is still a playable and good game, the tecnical problem of chaos gate are really hard (i don't talk about graphic but about compatibility) chaos gate need a gog version, same for final liberation.