Almost to 60 on the wizard. I'm in A3 of Hell (previously I said I was in Hell - I meant, of course, Nightmare).
It's definitely getting more challenging, but that's great. Normal/Nightmare was a bit of a joke. It required almost no strategizing.
I'm at something like 50K health (which is probably pretty pitiful), and nearly 20K damage (which is probably not all that pitiful all things considered).