Yeah my mate and I did 28 and 32 as a two - someone left us both times!
The Cabal boss with the interchangeable shield is the most difficult I have come across.
The thrall knight was easy, there is a place at the back where you can stand on ledge and peak above some cover and let some ice...
The horde mode has little objectives embedded into each round.
Makes it pretty tough, but better than finding a corner and keeping smashing the Song of Ir yut.