I think the main issue with 4's settlements out of their quantity is the relative lack of diversity in presentation and occupants. This is criticism you can apply to Fallout New Vegas to some extent, with a lot of towns forming in reaction to quests being written and designed first, but I digress.
Fallout 3: Paradise Falls (Slaver settlement), Little Lamplight (Child settlement within caves), Rivet City (Aircraft carrier), Megaton (Built around a bomb), the Citadel (The Pentagon), Tenpenny Tower (rich people oasis), Republic of Dave (Larp-ville), Arefu + Meresti Metro station* (Overpass highway + "vampires" in a metro), Underworld (Ghoul city), Big Town (Teenagers...? It has a moat), Canterbury Commons (Caravan hub), Temple of the Union/Lincoln Monument (slave sanctuary), Girdershade and Evergreen Mills** (Nuka Cola fanclub and Raider settlement)
*I combined those two because they lean on each other and Arefu has no merchants if I remember right.
**These barely counts, but it's on the same tier as most of Fallout 4's settlements, but they have a unique aspect/item/merchant and are technically settlements in-game.
Some of Fallout 3's settlements you'll never visit again after completing their associated quest or would otherwise be a decent place to get supplied if they weren't inconvenient. Meresti has a merchant but it's not worth the hassle of going through the metro again just to get there. Paradise Falls is great but their arms merchant requires 20 Chinese Assault rifles before their stock is as good as Flak and Shrapnel already is out the gate, but he also has the best repair in the game if I recall correctly. There's also a doctor on the opposite side. Tenpenny Tower is also pretty good but you'll lose access to the convenient merchants if you do the quest associated with it. In the odd situation you: blow up megaton + let the ghouls in, you're effectively leaving yourself with a single convenient spot to do all your shopping and healing (Rivet City).
Still, pretty good and diverse assortment. The most boring/never-again (after tie-in quests) are: Arefu, Meresti, Republic of Dave, Canterbury Commons, Temple of Union/Lincoln Monument, Girdershade, Evergreen Mills, Big Town. If I'm forgetting any then they'd just go here anyway.
I have a soft spot for Big Town despite it being shit by most criteria. I think I just like the quest.
Fallout 4 (sans most player settlements): Diamond City (stadium), Prywyn (BoS airship), Institute (underground/high tech), Railroad HQ (Church basement), Covenant (Walled town), Atom Cats garage (Power Armour garage), Graygarden (Mr Handy-worked greenhouse), Vault 81 (inhabited and active vault), The Slog (ghoul-worked farm), Goodneighbour ('character' - robot arms merchant, memory den, Hancock, etc), the Fort (Minutemen HQ + artillery + 5-star fort + minutemen radio), Bunker Hill (merchant hub + a famous monument).
Greygarden/The Slog don't have much going for them in the way of services until you add to them to your settlement roster, but they were included for having notable occupants even before you can customise them. The Fort was added more out of pity but it still has something going for it over most other settlements so I'll include it.
Immediate standout for being relatively unremarkable is Covenant. Fallout 3 had lots of settlements which were just a means to facilitate quests, such as Arefu, but there was some aspect of it that made seperated it from the rest. Covenant has walls and a notable robot like Diamond City, Vault 81, Goodneighbour. The GOAT exam entry requirement is neat fanservice but otherwise it's a Fallout 3 quest settlement sans any distinct visual tied to it and characters within. It being one of the few non-player settlements with a healer and merchant puts it on a select list but its spot on that list comes with nothing notable beyond its equally forgettable quest.
Bunker Hill I consider bizarre because you could've done a better version of Canterbury Commons (investing in merchants, increasing stock) but you can do no such thing. They could've done more with this, but to due its status as a settlement-to-be, the characters here can't be standouts due to them all being potential residents of a player settlement further down the road.
Fallout 4 has fewer "never again" settlements, but on a smaller list of actual settlements you're looking at a rather small list. Keep in mind you can further shrink that list if you side with the Institute, potentially losing the Prydwyn, Railroad HQ, and even the Fort if you want to. You lose the Institute either way if you join the others.
Of the true settlements:
The Prydwyn is cool, arguably the best settlement in 4.
Diamond City is probably the most disappointing but has characters of note. (the security wearing baseball gear makes sense, but why'd they do so much to hide the face, shouldn't the default show it but the 'heavy' variant hide it?)
Railroad HQ is shit. One somewhat likable character.
Institute is boring (not having any 'character' makes it easier for players to blow it up in the end, if the Institute had too much going for it the choice would actually be hard).
Covenant serves zero purpose and should kill itself.
You don't want to overload with choice, especially if you put so much work into an area and the player only visits it once because another option is preferable, but it does a lot of damage to the overall quality of the world if you do this. Fallout New Vegas arguably contains as many "never again" settlements/inhabited locations as 3 but even mundane places like the I88 reststop help serve the worldbuilding. Covenant serves zero purpose. It's like an even less notable Tenpenny Tower with an even less notable quest.
Fallout 4 technically has the most occupied places but many of them don't even have economies until the player creates one for them. There's pre-occupied settlements that don't produce enough water to provide for the occupants until the player creates water sources for them, it's just hollow.