arkham city for pc isn't out yet but. it out in 9 days for pc. i suggest to buy the game if you have money. it's a great game like starcraft 2, deus ex and elder scrolls skyrim. if you need to pirate something pirate modern warfare and similar 5 hourl "long" campaign for 60 bucks.
People usually torrent games without multiplayer (because you can't play multiplayer with torrents unless you use hamachi or tunngle, but the population is terrible), and buy games with multiplayer.