I just got to Act II, in Inferno, with my Barbarian.
I... can confirm that from this point you either just blindly keep going because you really feel like it, or you pretty much start leveling a new class. To be honest I didn't necessarily expect that myself, I read about it from other Barbarian players whom also got to Inferno but I was still playing Hell a few days ago. I would say that the first Act is very "do-able", but Act II is a nightmare (well it's an inferno now). I literally got two-shot by a Sand Wasp right from the starting quest when we meet the Enchantress, and I laughed. I changed my skills around a bit but... even if I do have an "Act II-efficient" build going I'll still need much better gear from this point.
I do 28.7K DPS, of course about double that from critical hits (around 60K I think with crits since I have some crits damage-enhanced rings), got around 5.2K armor with WarCry + Impunity Rune (resist non-physical damage by 20%). The thing is I've always been playing all that time with a 2-handed, I went with Maces for increased Critical Hit chances (I'm at 43% to crit). It worked well in Act I, but I found myself using many single-target-focused skills more than anything else. I usually go with Cleave + Rupture for AoE, worked marvelously well from Normal to Hell, "well enough" I guess for Act I Inferno but I often had to switch to Bash, or going with Hammer of Ancients + Smash... that or also Charge + Ram (283% weapon damage at the targeted area).
Anyway, my play-style, my build, my gear... by now in Act II Inferno is pretty much going down the drain due to obvious inefficiency. I was of course expecting Inferno to be "ridiculously hard", but not that much really. All of my items are Level 59 or 60, most of them are Level 60, all of them are Rares with important stats and my Mace has 943 DPS on it (got it from the AH for only 80K Gold, go me). Now the thing is... even if I magically received a 1,500+ DPS weapon I would STILL need some godly armor pieces to resist anything. Speaking of which (resists), with WarCry I only have around 220 resists (not to everything, others are around 180 or so), so no wonder why those little poisoned wasps hit me two times and I die.
And, yes, Wrath of the Berserker is often needed... if not simply required to kill Elites, and I would say that it's something which applies perhaps even in the first Act. I mean in Hell I used it by choice, but in Inferno you absolutely need to have actual control over your DPS and where it goes, I can't rely on Earthquake or stuff that is fixed on the ground since I need to kite pretty much all Elite packs I encounter, so at least we DO have Wrath of the Berserker. I just wish we could have more liberty of choice when it comes to builds in Inferno, but I have the feeling that at least as far as Barbarians go we'll pretty much have to rely on maybe one or two "known" builds that are "doing better than the rest", if they do exist.
Anyway... I needed a break after just starting Act II, I have yet to finish the first map to find and interrupt the cultists, those Wasps (not even the main Wasps, but their little ones going in a straight line) and I'm sure many other mobs will give me a hard time. At least I did level up two other classes, I have a Monk and a Demon Hunter, both are Level 54 in Hell Act 1 so... I think I'll give a go with a Demon Hunter. I feel that if I ever want to give a more serious try to Inferno I'll definitely need to leave my Barb behind until I farm items (or Gold, to buy them) with another class first, and then perhaps gear up my Barb for Inferno from that farming.
Any other Barb players feel the same in Inferno? Anyone got a "good enough" build for it?