Sharpshooter
ignore range, ignore cover, "greatbow mastery" (the -5/+10 bit)
Design: Where to start? This is the most generous feat in the whole book. Even if you feel Great Weapon Master is completely balanced and unproblematic, you should give pause before approving this one: it gives the best aspect of a greatweapon at incredible range. I understand that the designer wanted a simple way of saying "you can shoot longer and more accurately", but a complete negation of range and cover removes an important part of the game - the tactics and maneuvering. And even ignoring all of this, this isn't exactly a sharpshooter's feat. Nothing about this feat turns you into a William Tell. It just turns you into a combat monster in general. WotC really needed to playtest this more. The grade is still not red, since from a pure design perspective it's still a very simple and direct implementation.
Fun: While you could argue it's fun to pick off monsters that feebly try to take cover etc, I will grade this on the assumption that range and cover actually adds to the game.
Power: By itself this is good, and obviously gold for specialized archers. It is taken together with all the other changes to ranged fire this goes over the top. And it is with Crossbow Expert the game finally crosses the line entirely into a game where you no longer need melee. To grade that, I would have to get a new grade, sky blue perhaps?
Shield Master
bonus action shoves, add shield AC to personal Dex saves, use reaction to negate half damage on Dex saves
Design: Fairly okay. I find the AC save bonus needlessly constrained to effects that target only you. Also, it's a bit weird how this becomes (much) better with a +3 shield (which already is over the top). This could have being phrased either as you gaining advantage, or a +2 bonus that applies to all dex saves you make.
Fun: Bashing your enemy prone is a great way to embarrass it
Power: Bonus action shoves isn't as valuable as bonus action attacks (which can be used to shove); The AC save bonus isn't generously worded. Still, I hesitate lowering this into purple.
Skilled
3 skills/tools
Design: Rather straightforward. Rather conservative too - this could have been made more exciting you know...
Fun: Definitely enabling you to play your character
Power: Not so much combat power. Still not bad - if you take this, you probably will gain more from your new skills than +1 to attacks and damage...
Skulker
benefits
Design: Its not this feat's fault the Stealth rules have failed to yield a single consistent interpretation. Leaving this black.
Fun: Assuming this feat is what stands between you and carefree sniping, I would say, yes it is fun
Power: Hard to say. Some groups don't turn sneaking and hiding into a great deal, some do. I wouldn't pick this feat without first clearing up with my DM what, exactly, I stand to gain from doing so.
Spell Sniper
double range on attack spells, ignore cover, cantrip
Design: Doubling the range is very generous, but in principle this is better than "negate range penalty" (as for Sharpshooter). Gaining a cantrip is a bit strange - this doesn't benefit those most likely to pick this, since they already have the cantrip they want to use! Not seeing the clear design concept here...
Fun: Okay
Power: Not sure this is good enough. You already have good range on most cantrips, and there simply aren't enough good regular spells with attack rolls. Since none of my players have shown any interest in this, I'm tentatively grading this purple. Feel free to convince me it's better than this, though!
Tavern Brawler
improvised, unarmed; bonus grapples
Design: When I DMd this I remember we found it unclear. I would have preferred if the feat was more clear on exactly what it turns "improvised", the weapon, into.
Fun: Barroom brawls is fun.
Power: Not much. After all, all you gain is the ability to do nearly as much without a regular weapon as you're normally capable of with one. The bonus grapple is nice, though strictly a subset of what getting to use your bonus action for an attack would have given you. (As far as I understand, there's nothing here that makes you a better grappler assuming you gain access to a bonus attack bonus action from elsewhere) Take this to enhance roleplay, not to optimize your build. Since this is a half-feat, I'm not grading this purple.
Tough
moar hit points
Design: Straight-forward
Fun: Indirectly: staying alive is always fun...
Power: In 5E your level and power is first and foremost a matter of hit points. This turns your d8's into d12's. This gives you much of what a whole new level gives you. The grade assumes you've reached at least the mid levels; at low levels there are much more important things to take.
War Caster
advantage on concentration saves, no free hand needed, cast spell as OA
Design: I dislike the cluttered implementation of hand usage, but that's the subject of another discussion. The language could have made it more clear this is the way casters get to use cantrips as OAs.
Fun: Is okay
Power: Not an inconsiderable deal to make Concentration checks at advantage. The hand use thing is mostly minor. Spell OAs is nice.
Weapon Master
4 weapon proficiencies
Design: This needs a redesign, much like armor proficiences
Fun: I guess.
Power: No. Saved from red by the half feat.