Chris and I played through the whole thing on Legendary. There were a couple of tough spots, but we made it through pretty quickly. Maybe three or four of us could play a few Acts this weekend with the difficulty turned up.
The toughest spot on Legendary I think is the spot on Tsavo Highway when you cross the broken section of highway and have to face off against waves of Brutes, Jackal snipers and the Wraith. I always end up just rushing forward in order to get the next checkpoint so that they disappear. I must have spent 3 days trying to do it before just running.
I should be around most of the weekend so whenever works for me.
I'm up for playing some games with other people. I've got Army of Two, Burnout Paradise, Call of Juarez, Frontlines: Fuel of War, Halo 3, Turning Point: Fall of Liberty, and WarTech: Senko No Ronde.