I completely agree, Morbid Curisoity, is by far the Hardest of the Trophies to obtain, (Undead is relatively easy on the first level).
I reccommend Co-Op with someone next to you or a Mic On-Line, for Morbid.
i tried Co-Op with no mic, and it made it harder.
The Graveyard, end is by far the hardest level in the game.
I found that the final part of Highway to hell is really easy with the Flare + Blade Cannon combo, particulary against soldiers.