Far Harbor is genuinely worth it. The actual main campaign is short but the island is fun to explore and it has, who would have thought, actually good writing that touches on the themes that Fallout 4 seemed to be trying to examine. It also has quite a few choices, a few skill (well, SPECIAL and perk) checks, and you can play the main character in tons of different ways. It also has the best designed armor in the game and some really unique weapons (although the Lever-Action Rifle kinda sucks).
Nuka-World is really just an explore and shoot-em-up. It has some good items, but don't expect a good story, lots of choices or even well designed mission structure. It's almost all "go here, kill x." They also made a baffling decision that I won't spoil you on, you can look it up if you want to.
Automatron's story is decent for what it is. The robot building mechanic is pretty good, I found myself using it here and there. It also adds the Tesla rifle back in the game, but it looks nothing like it did in other games.
None of the workshop DLCs are particularly good. I find myself using Wasteland Workshop items the most, then Contraptions, and then finally I pretty much never used the Vault-Tec shit (which you can only use one area anyways) after its """story""" was over. Personally I wouldn't recommend any of them if you're buying individually. Wasteland might be worth it, but I'd look up what it adds first.
The Railroad are SJW scum
Remember when that Institute guy that helped them committed suicide after his life was ruined and they
lied about it?