I think part of the problem with 5E feats are that most of them just don't give you enough "stuff" for their purchase to make it feel like its worth taking. Not when you only get to make 1 or possibly 2 total selections since most games don't end up reaching 12th level anyway. And then on top of that, one of those two selections usually ends up being an ASI.
Case in point, the Grappler and the Tavern Brawler feats... both of them enhance what those different aspects do (grappling and improvised/unarmed combat)... but neither of those things are done enough in the game to make it feel like you're actually getting something worthwhile for taking the feat. When I re-did a lot of the feats for my game, I just thought "Are either grappling and unarmed/improvised weapon combat so overpowered that it would kill me to give someone both feats?" And the answer was 'No'. If someone in my game wanted to be that kind of person who forsook their weapons (and all the class features they had to enhance them) in order to grapple and brawl... then just them go wild with it. So I combined the feats together and made:
BRAWLER
- You are proficient with improvised weapons and unarmed strikes.
- Your unarmed strikes and improvised weapon attacks use a d4 for damage.
- When you hit a creature with an unarmed strike or improvised weapon on your turn, you can use a Bonus action to make an unarmed strike or attempt to grapple the target.
- Whenever you make a STR (Athletics) check to grapple a creature or escape a grapple, you are considered proficient in the Athletics skill and add double your proficiency bonus to the check.
- You have Advantage on attack rolls against a creature you are grappling.
- You can use your Action to try to pin a creature grappled by you-- make another grapple check and if successful both you and your target are Restrained until the grapple ends.
Now neverminding the fact I'm sure there are optimizer players out there who will see this and immediately formulate sixty-five different ways to break the game using my feat above... for my normal players in my normal game, it actually gave the person a whole heap of stuff for taking the feat. All kinds of cool, small stuff they could do. And that's what I wanted-- a feat that boosts many small but similar isolated parts of the game to really make it feel like this person
is that kind of person. This person is a brawler... because they get to do a whole ton of brawling stuff and get brawling bonuses that others don't get.
On a similar note, I found the Athlete and Mobile feats to both have some nice ideas... but not nearly enough to feel like it'd be worthwhile to forsake an ASI or combat feat for them. So I combined and edited both of them as well to really give you a highly-mobile character if you took it:
FREERUNNER
- Your speed increases by 10 feet.
- You may use a Bonus action on your turn to take the Dash action.
- Difficult terrain doesn't cost you extra movement.
- When you are prone, standing up uses only 5 feet of your movement.
- Climbing doesn't halve your speed.
- You can make a running long or high jump after moving only 5 feet rather than 10.
- When falling, you may reduce the distance fallen by 20' for the purposes of calculating damage.
This is something that an athletic-focused character would actually enjoy taking, and would definitely make this character feel different than the other PCs. They get a lot of really good meat that might only occur in isolated circumstances, but will be exceedingly useful when it does.
And then for the smarter group of PCs out there... I combined two of the lamer feats together, Linguist and Keen Mind, plus added in a bit from Observant to give the character a lot of stuff to get for spending a feat slot:
LINGUIST
- You may learn three languages of your choice.
- You can ably create written cyphers, and whenever you make an INT check to decipher a code or puzzle you are considered proficient in the applicable skill and add double your proficiency bonus to the check.
- You can communicate simple instructions non-verbally to allies that can see you and share your same language.
- You can read the lips of creatures you can see and whose language you understand.
- You can accurately recall anything you have seen or heard within the past month.
I can understand why they decided to lessen the power of the feats... because they didn't want things at the very beginning of the game's life to go really far off the reservation because they didn't know yet what was going to be truly important. So doing things like a couple small abilities plus a half-ASI was probably a little safer. But now all these years in... we know that if you are taking a feat its because you want to make your character stand out from the others in the group... and a half-ASI doesn't lend itself to that. That's just the same as anyone could and would take. So instead, I just let my players go all-in on the specialty stuff they wanted to do. And for the most part it worked out.