You get to quest through various cities in the Empire, discovering new destinations and dungeons as you complete quests and slay the bad guys.
You start out with the traditional 4 characters, the barbarian, the elf, the dwarf and the wizard and there is an option to buy 3 different characters if you wish at $3 each (I think). The game itself cost $5 to download so the new characters do seem a little expensive, but fortunately they are not a requirement to play the game. Game play is turn by turn as per the board game with all the rules in place. You don't get to see the dice rolls which seems to upset some people but it really doesn't bother me, actually I prefer the game without an artificial dice roll occurring.
After crawling through various dungeons and emerging battered but victorious you can return to one of the settlements nearby to level up your heroes and buy new equipment and provisions. There are several difficulties you can play on which allow you to recover dead heroes or play on the hardest mode where a dead hero is dead for good - you can still recruit a new rookie hero from a settlement and hope they survive a little longer.
I believe there are several other GW games that are being ported to the iPad, Space Hulk being one of them. There are so many GW turn based games that are simply crying out to be converted into the digital realm that I see a bumper crop of toys ahead of Oldhammer gamers.