My character isn't "mine" any more. The only real way to progress is to grind for loot now. Or pay someone for it. (something my friends and I never did in d2)
I know that my skill set changed pretty radically on subsequent difficulty levels, the same tactics didn't work terribly well.
In D2 I'll admit the skill tree had some severe flaws, but it allowed unique customization to an extent.
Diablo 3 seems to have an entirely different curve where progress diminishes to near uselessness until you get a lucky loot drop and you can finally make headway again.
In Diablo 2 there was always a "sweet spot" where you could earn maximum experience and you never seemed to be so woefully under-equipped. A surprising drop would mean a big boost in performance for the next few levels, always a treat, but if you didn't get one you could still do okay.
In Diablo 3 the theoretical sweet spot is always way ahead of what your gear can handle and you're left struggling, out of your league, or coasting in a less difficult area with near zero experience awarded.
It's just not tuned right, unless of course the idea is to drive people to the Auction House.
How many hours do you expect from a "complete game"?
I've now played through normal, nightmare and hell with my main character and have the mindset that inferno isn't really part of the game. I see it as a "turn the difficulty knobs up to 11 and force the unlucky people to buy things on the auction house".
Even if I decide that inferno isn't worth the hassle I've played roughly 60 hours on that one character.
I found that there was enough "hey, that didn't happen last time!" moments that the 2nd and 3rd play throughs were enjoyable.