Now personally I loved it and still do. Yes, there were some problems, but nothing that couldn't be overcome in the same way that we overcame any sort of problems with the rules that came before and after. We tinkered. Indeed, one of the features of my own Adventures Dark and Deep game is that the rules seamlessly integrate the original 1E rules and the material from UA, plus additional new material along the same lines integrated into the whole. Admittedly, I did make tweaks to the whole along the way, but it would not be inaccurate to say that if you wanted to see barbarians and acrobats alongside illusionists and druids in the rules, ADD will sate your appetite.
I'd like to specifically examine the barbarian class, and posit that the class itself is not unbalanced, overpowered, or anti-social. It is simply intended for a different sort of campaign than most DMs were used to at the time, and suffered from a lack of supporting documentation regarding this fact.
Bear in mind that Gygax's own campaign was rather magic-user-heavy. There were occasional stars of other classes, such as Robilar the fighter, but the real luminaries were the high-level magic-users, either played by Gygax himself or others, that stole the show; think Tenser, Mordenkainen, Otiluke, Bigby, etc. I think Gygax was deliberately trying to point the way to something 180 degrees away from that model.
I think the class itself implies a non-magic-user-centric campaign.
The barbarian class assumes the existence of barbarian homelands. Not necessarily a Viking-esque locale, because there are examples from steaming jungles and broad Mongol-like steppes given in the text. But there has to be a barbarian outland whence the barbarian can stride into civilization and tread it beneath his sandaled feet.
As further evidence, I point you to the Hunter character class, which Gygax wrote in 1988 after his ouster from TSR. I had actually seriously considered including a hunter class in Adventures Dark and Deep, but finally came down on the side of leaving it out because of copyright reasons as well as the fact that it was never listed as one of the new classes that Gygax was considering at the time his 2nd edition was being contemplated. But look at some of the background text of the class:
The hunter is one who was born in a wilderness area and grew up in primitive conditions requiring a knowledge of woodcraft, fishing, trapping, tracking, knowing the flora and fauna for many reasons, and hunting to sustain life. There might be rare exceptions to this, but generally the hunter is one of savage, barbaric background. There are, of course, hunters from open plains areas, frozen tundra, and barrens. Such individuals are of more nomadic sort than the class considers, and in general these backgrounds are more akin to the barbarian class. The hunter class considers a wooded homeland as the principal training ground, and this should suit most campaign milieus.There are specific call-outs to the barbarian class in the mechanics, too. Armor and weapons, and weapon specialization, work the same for the hunter as they do for the barbarian. In fact, there seems to be very little daylight between the barbarian and the hunter except in the combat skill area. (Although as an aside, the lack of any actual hunting skill for the hunter class is somewhat... odd.)
In the World of Greyhawk there would be several excellent places for a barbarian campaign to be set. Ratik, that frontier of civilization on the edge of the Thilronian Penninsula, Tenh, which borders both the Rovers of the Barrens and Stonefist/Stonehold, and possibly even a Vesve Forest/Highfolk/Perrenland campaign, with both Tiger and Wolf Nomads to serve as wide-eyed visitors in strange civilized surroundings.
Even if that wasn't Gygax's conscious choice when putting together the barbarian class originally, and certainly this is all speculation of the highest order, I think the much-maligned barbarian could be redeemed by looking at him in that light. A group of barbarians, thieves, hunters, and fighters, coming down from the fringes and into civilization, might make an excellent theme of a campaign, and would even recall the standard set-up of MAR Barker's Tékumel, which placed the PCs as barbaric visitors into the decadent splendor of ancient civilizations.
I think it could work.