I've been liking most of the changes in the two UA documents released so far. I had a lot of hangups about the rationale for getting rid of racial ability modifiers at first, but once I tried to look at what they were doing with an open mind and realized that those were only minor changes that you could effectively turn back anyways by using custom backgrounds to assign ASIs based on the old race modifiers if you wanted to, and that mechanically this approach was preferable as well, I was able to get over it. And a lot of the other changes were more to my taste, though, I have mixed feelings about some and I'm not entirely sold on some of the feats in the most recent document.
I prefer the consolidation of spell lists into just three groups, because it minimizes bookkeeping and I always felt that class specific lists were largely arbitrary anyway. And specific classes may still get access to some select spells from other lists, and/or have access gated by schools instead (Bards, for example, now get access to just Divination, Enchantment, Illusion and Transmutation spells, plus a few healing/restoration spells from the Divine list), so there's still some degree of distinctiveness between spellcasting classes, they just don't over complicate spell organization to achieve it.
I also like how everyone gets a feat as part of their Background now, which is something I've been thinking about doing anyways—now it's just official. I also like the feats covered in the Character Origins document, but I'm a bit iffy about the ones in the Expert classes document. The expert feats just seem arbitrarily gated to level 4 for no apparent reason other than to complicated feat access. I can sorta understand them gating Epic Boons to level 20 (they're supposed to be "epic" and are a bit over the top), but there's zero reason to gate any of the other stuff to level 4, that I can think of at least.
I also hate what they did to Dual Wielder. They effectively nerfed it by getting rid of the wimpy +1 to AC, and you're no longer able to use a weapon without the "light" property in each hand—the one in your off-hand HAS to be light now, cuz wielding a heavier weapon in each hand is apparently an impossible feat, I'm somehow able to pull off in real life (not that it's optimal, but it definitely is doable). You now get a +1 to Strength or Dexterity instead, which is the laziest workaround for handling weak feats I've always hated about 5e. It's like they have no clue WTF to do with dual wielding, so they had to make it worse than it already was. Meanwhile Great Weapon Masters now get a +1 to Strength on top of getting to keep their old Cleave ability, and also get to add their Proficiency Bonus to one attack per round without needing to take a penalty anymore.
There's probably other stuff I like or don't like, but that's what comes off the top of my head.