When UA came out my group was famished for new 1e content. We were playing with material from Dragon but a new book was special and OFFICIAL!
In the end, we only really used weapon specialization, some of the new weapons, the expanded race/class options, and the new spells and magic items. The expanded illusionist spell list was especially welcome. The barbarian got some use but got dropped once players realized it only had defensive abilities and that a specialized fighter was kick ass. The cavalier got some initial love for the potential stat increases but no traction. No one in my group ever made an acrobat. Some of the lore was great but we already had it from Dragon.
Rules that actually made AD&D worse:
- Comeliness
- Subraces with better attributes or powers than the PH races
- Barbarian incentive to destroy magic and disrupt the party
- Paladin as a subclass of cavalier putting it even more out of reach and linking the holy warrior to social class
- Cavalier with an incentive to drag the party into TPK fights
- Forcing ranger and paladin/cavalier into specific weapon proficiencies for no good reason
- More complicated spellbook rules
- Forcing illusionists into the same naughty word dependence on read magic that MUs had to live with
- Weapon specialization locking in at 1st leveln and creating an incentive to not use magic weapons
Some of these are easily fixed. In my AD&D campaign I permit retraining weapon proficiencies, including specialization, along with training for a new level, and I don't permit double specialization. I've also considered just delaying it until after first level.
This is exactly the conclusion that our group came to as well. The Barbarian only worked in a 1-1 game and it's slow advancement made even that a pain. The code of conduct for the Cavalier made playing one a death sentence. The acrobat abilities should have just been given to the thief whole cloth.