I only got this game recently having heard many good things about it and was rather dissapointed to find that there were only 12 missions and id completed it in about two days. However i was bored one day and picked it up again and found myself reimmersed in what is a fantastic gaming experience.
You play mainly as the Space Marines, a bunch of uber-tough killing machines. Although if you feel like skirmishes or online play then you can play as Eldar (dudes dedicated to the preservation of the universe), Orks (dudes dedicated to the destruction of the universe), or Chaos Marines. (pretty much the same as space marines exept much more evil, and fun)
Unfortunately there is only one campaign mode (as the Space Marines) but at least it is well structured and provides better opposition than skirmishes.
Overall not a game i'd play religiously but good fun when i feel like something different and with plenty of unit upgrades promised for winter assault and dark crusade this will be a game ill find myself coming back to.