UltimateUnknown on 09 September 2014
I'm playing the game right now and there are strike missions you can do which are optional. With those added together you can probably easily double the time from the basic run. Plus the replay value is quite good, especially going back and doing the missions on hard difficulty once you've leveled up a bit.
This is of course not taking into account crucible pvp, which in itself is massive. Bungie are known for their excellent MP.
