In the Character Origins UA we got roughly a month and a half ago (I think?) we got a number of 1st level feats - these are feats that players can takes as part of their background (or a second one if you play a human,) and the general intent was for them to be impactful but simple - things like Tough, for example.
The Expert Classes UA brings in a number of new feats. These are "4th level" feats, which means that you can't take them until you hit 4th level, when each class gets its first feat.
In addition to this, there are two other categories of feat - Epic Boons and Fighting Styles. Epic Boons are, essentially, 20th-level feats. Each class' old capstone ability is now gained at level 18 (though I imagine Paladins will be shuffled around, given that their old capstone was a subclass feature, and subclass feature levels are being standardized to levels 3, 6, 10, and 14) and now level 20 is when you get a free Epic Boon, which is a feat that's meant to be particularly huge.
Fighting Styles are special feats that Warrior classes (Barbarians, Fighters, and Monks) get, as do Rangers, despite being Experts, and presumably Paladins, despite being Priests. (I find this rather interesting given that in the 2014 PHB, the only "warrior" class that gets Fighting Style is the Fighter).
The way these work is that 1st level feats, Fighting Styles, and 4th level feats are all added to the pool of feats you can pick up as you level up and get more feats. If you hit level 8, you could take one of the 4th level feats that are generally designed to be the ones you pick up on your leveling journey, but if you feel a strong desire to get another 1st level feat or Fighting Style (and meet the requirements) you can choose those.
But, before we dive in, we should make a couple notes:
The first is that the Ability Score Improvement feature is now a feat. It's presented as the obvious, default choice for feats, but it's now considered just a first among equals, rather than a totally different game mechanic. It works the same as it did - you can raise one ability score by 2 or two ability scores by 1, to a maximum of 20.
However, you might be less inclined to take this for the following reason:
Every single 4th level feat (and again, remember that that's just a minimum level) comes with a one-point ability score bonus.
The upshot of this is that feats like Great Weapon Master (which works a little differently - let's wait to see the full picture on weapon mechanics before we lament the loss of the -5/+10 mechanic) now inch you along toward a higher Strength modifier - you're going to hit 20 strength later if you use these feats instead of the Ability Score Improvement one, but you can still get there eventually while picking up some awesome features along the way.
Feats can certainly feel costly the way the game currently works, but this encourages players to use them a little more, and I actually think you'll probably see some very powerful character builds that take a non-ASI feat every time.
Now, the full list of feats is far too much for me to go into every tiny detail. I'll highlight that I think Heavy Armor Master is way better now (reducing incoming bludgeoning, piercing, and slashing damage by your PB, rather than a flat 3, and also working on magical weapon attacks).
Also, several feats now include the "no disadvantage from ranged attacks while in melee with an enemy" that Crossbow Expert has - the odd thing that would often encourage spellcasters who'd never use a crossbow to take the feat. This is now rolled into both Spell Sniper and Sharpshooter (the latter of which, like Great Weapon Master, also no longer has its -5/+10 feature).
Fighting Styles' only requirement is that the character be a member of a class in the Warrior group - though Rangers, despite being Experts, can also use them (presumably Paladins will get a similar exception despite being classified as a Priest class). While I have no trouble seeing how Barbarians will benefit from having Fighting Styles, I'm curious to see which will look the most appealing to Monks (obviously, we're getting the Ranger-facing Fighting Style feats right now, so look forward to the Warrior UA for more). Among the options here, which are Archery, Defense, Dueling, Great Weapon Fighting, Protection, and Two-Weapon Fighting, the only one that I could imagine being useful for a Monk would be Dueling (most work as they normally do, though Protection is a little different).
Epic Boons are also limited by class group - as such, we're really only seeing the ones with no prerequisites or that are available to Experts.
In a very real sense, these are "level 20 feats," and while obviously in most situations you're not going to have other opportunities to pick them up, as with the old Epic Boon mechanics, if you earn a bunch of XP at level 20 (or, I suppose, you hit milestones your DM deems appropriate) you can get these multiple times.
While the level 20 feature is not simply "feat," it effectively is - you can choose lower-level feats to pick up at 20 if you really want to - though I think the Epic Boons are strong enough that you would probably be best off taking them. (Interestingly, the Epic Boon of Fortitude raises your max HP by 40, which technically makes it identical to the Tough feat given that you're level 20 - but you can pick up both, raising your max HP by 80 total if you want to be an absolute damage-sponge). (This one actually exists in the DMG already).
As a last little observation: Lightly Armored is a new 1st-level feat added in this UA. It's significantly buffed - it now grants Training (a new term for being able to use armor, given that "proficiency" with armor didn't use your proficiency bonus) with Light as well as Medium Armor and Shields. Essentially, this combines Lightly Armored and Moderately Armored from the current game. I actually think this is huge, because some classes really struggle to get a decent AC, especially if they're not a Dexterity-based class, and taking this feat at level 1 makes it pretty easy to get an AC of 18 from the word go.
As is evident here, feats are obviously no longer an "optional rule" in One D&D, which is probably fine given that I don't think I've ever played in a 5th Edition game where they haven't been allowed.
In the long run, I think this will make it a little more challenging for new players to build their characters, even if it doesn't technically make things more complicated than they already are. I love that 4th-level feats come with an ability score bonus, as it makes them less punishing to pick up. But at the same time, that makes it harder to ignore them and just go with a full ASI.
Still, I think this is a net positive for the game.