If you are able to stick to the game => The after game BF are pretty tough. Enemies range from 2 levels lower up to 1 lvl higher. In this case they are really dynamic.
Enemies in Act 3 in-game are harder (try killing the humans there, they use magical attacks) - and those in Act 4 BF use the stunning Shaman hammer spell. Maybe this will challenge you a bit?
Kiya
BTW, I played the game without BF (just went in there afterwards for trying out stuff). I couldn't say it was too short - but maybe this is only my opinion.
