If you're over 30 and still live with your parents then there's a fair chance you'll be familiar with the world Warhammer 40,000. For the rest of us though, Dawn of War will be a first, and very pleasant, introduction to the Space Marines, Eldar and Orcish hordes that made the tabletop game so popular.
Based in traditional RTS territory, Dawn of War makes a few changes to the tried-and-tested formula. Resource gathering is abandoned in favour of capturing strategic points on the map - ownership of which diverts credits to your coffers - and more powerful units require the capture of far-flung Relic points. The unit balance has been carefully set too, boosting the usefulness of Terminator Marines, Death Jesters and the other faithfully-replicated infantry types.
The various races are suitably different to play and well (though you're limited to Space Marines in the single player campaign), and while ropey AI removes the challenge from offline play, Dawn of War is one of the most satisfying multiplayer experiences around.