I have to agree with Monk and Joker on this. I played Diablo 1 and 2, both online, both for many many years (D2 especially). I played Diablo 2 last night with my old barbarian stuck on the ancients in hell. It feels like a sequel to what we're playing now in D3, that's how much better I'd say it is. There is no comparison in terms of items, D2 trumps with the amount of variables you can get on your items. By inferno D3, it's pretty much resist, armor, vitality, life on hit and maybe if I get really lucky I can have some strength. The story was also a mess, it was okay overall, but the dialogue was cringe-worthy, wow. When I first played coop with friends I wanted them to chill out so I could listen to the story and dialogue, but eventually felt too embarrassed to make them listen to it.
I didn't mind the idea of the skills/runes at first, I thought it could work out but knew only time would tell. And at the end, their goal of "skill variety and freedom" fails hard, because you're stuck into a few combos. Even though D2 sort of forced you into some combos to max out, there's probably more of those combos than what my barbarian has to work with. The longevity is also killed by not being able to play around with skill points, learning from you mistakes, lots more spells you could cast, etc.
Last night I played that D2 barbarian for about 20-30mins, did some Mephisto runs and honestly, it was much more satisfying than any butcher run will ever be in D3. Because awesome stuff dropped, even though I had no use for any of it, it was awesome and I wanted to keep going back for more. Then the extras like mods, offline, 8 players, etc. makes D3 not even in the same bracket as D2.
I'll still play the game until I beat inferno with my barb, I've also got a hc character which is way more entertaining and currently in act4 normal. The game's definitely really good and no doubt massively addictive and fun, but it flops hard in comparison to Diablo2 and won't last a quarter as long for me, which is sad, because this was the game I wanted to play for the next few years at least and even with the online stuff I didn't care and had really high hopes.