Nightmare difficulty with my Monk (Capuchin. Get it? A Capuchin MONKey?) has proven fairly easy. Jon, if you're reading this, you probably doubt me when I say that due to how many times I died when we were playing, but with a quick gear fix everything is smoother sailing. I have been reading up on builds and how to optimize things for my class, so I will probably have a powerhouse when all is said and done. I have gotten barely past the Skeleton King in act 1, and I'm at level 37. I've amused myself going back through and playing boss fights in Normal with my monk now. It's uncanny just how much easier 4 levels makes Izual and Diablo. Izual was down in 30 seconds, Diablo in about 2 minutes.
In other news, I gave my wife a guest pass and she loved it, so she's now playing with me! I started up a Demon Hunter (Winchester, named after demon hunters Sam and Dean Winchester from Supernatural) since she was interested in Monk, so we have some melee and ranged going. I'm up to 25 on my Demon Hunter and loving it so far.
When I'm playing DH, I think I prefer it to Monk, until I switch back to my monk. That's one awesome thing about the game-- everything (so far) feels fresh. New difficulties and new classes that fundamentally change gameplay make the same content you've already played feel fresh again.
Demon Hunter was a bit tricky, at least at first. Every death was a learning experience, but early on death came quickly and often. Now I'm a badass as long as I don't get in the middle of a pack of elites.
I'm looking forward to seeing how they both play out.
EDIT: Also, click the image for a pretty badass wallpaper.