Well, I hope that with idstudio we can create some more difficult levels.
Playing the Wasteland Legend missions Solo, on Nightmare, is pretty tough, but still fun.
Also, just now I tried to do Mutant Bash on Nightmare with fist only... I got up to the spike room, and one of the spikes instant killed me. I'll try again later. I'm sure I'll need to pull out the shotgun once the Kraken comes out though.