I'm getting close to finishing Hell with a second character, a Barbarian. Level 56 with decent gear. My armor class is unimpressive and my resistance practically non-existant but I'm still plowing through Hell mode with great ease and still mostly dying from cheap shots post-mortem abilities like Molten mobs exploding or a bunch of Arcane enchanted mobs leaving orbs that kill me while I finish off the pack.
I read a statement from Blizzard saying that they were currently going through the Inferno mode, nerfing a couple of skills and were fixing a couple of other balancing issues. All in all, I'm close to having two characters at max level and both in Inferno mode after two weeks of playing, that's just incredible compared to Diablo II, I never even once got a single character to max level since Dying actually had consequences and even regular mobs presented a challenge and you couldn't good gear off of the auction house.
I like the game, there's no doubt about that, otherwise I would never spend so many hours playing it, but it is way too simple as it is and when I called bullshit on Blizzard's infamous "we tweaked the difficulty until the testers said stop and then doubled it" and it seems I was absolutely spot on (or Blizzard have shitty testers).
I still think the overall skill system is a mistake, my character wastes two stat points every level that I could have poured into my primary stats and the fatc that everyone can do everything completely removes the incentive for starting another character of the same class that you've already played, this is one of the key factors that made Diablo II so endless. Titan Quest also had this pegged with their brilliant skill and stat system.
One more thing; the items. Not the fact that Rare's and even Magic are better than Legendary but the items themselves and theor nonsensical stats at times. Bows with only massive Intelligence boosts, Witch Doctor daggers or Mojo's with massive Dexterity boosts and generally items with one terrific feature and several shitty ones, being pawned off for insane prices at the auction house (that sometimes stops functioning).