Well-prepared for the future.
I honestly haven't been paying much attention to Fallout 4's DLC. I'm not much of a builder or community organizer in the game, and my main focus in the Minutemen missions was to use them to level up my character or explore nearby areas. So the prior build upgrades didn't have much appeal to me, and I hadn't set aside the time to play Far Harbor since the game's main story decision at the end left me with a bad taste in my mouth.
So it was surprising, when I sat down to play the Vault-Tec Workshop DLC how much more engaged I felt with the game, and how its surprisingly fun little story complimented the addition of Vault-Tec tilesets and accessories. The Vault-Tec Workshop DLC approaches the whole thing with the best of the series' wry sense of humor.
With the DLC installed, on reaching level 20 the Sole Survivor picks up a new radio distress call from Vault 88. Upon further investigation (and removing some Raiders from the vault door), you are met with another pre-war survivor, Overseer Barstow, the only non-feral ghoul left in the vault, whose location was chosen for radioactive material that could be mined for its experiments.
This quickly evolves into two quests: the first is clearing out the cave-ins and hostile occupants of the vault, including some wasteland heavy hitters, to make space available for growth in The Vault. At level 20, each of the three major caverns constitute an extreme challenge and had I not acquired a Fat Man and quite a few mini-nukes on the way, I almost certainly would have been killed by the Legendary Radscorpion, Legendary Alpha Deathclaw, and Mirelurk Queen who all waited at the end of its cavern as a boss
The second major quest element is helping Overseer Barstow fulfill her mission of carrying out her mandated experiments for Vault-Tec. The experiments are relatively tame in terms of Vault-Tec's history, though Barstow urges you to be as devious as possible in carrying them out on an unsuspecting and trusting new Vault Dweller named Clem, who is just happy not to be attacked by molerats.
Each of the experiments centers around creating new devices, which either coerce NPCs in some way to be more efficient or improves morale but with less direct resource benefits for the vault. Upon completing each of these experiment quests you can build those devices at any of your settlements. An example of these devices, featured in advertisements for the DLC, is an exercise bike that can be used to generate electricity. You can choose, at the Overseer's urging, to have it give people electric shocks if they go too slow or just let them use it normally. If you choose the electric-shock method, the bike will generate more power, but won't do anything to make your people happy.
For one of the devices, you are sent outside the vault into the ruins of a chemical company called "HalluciGen" to retrieve a chemical formula that was supposed to be delivered before the bombs hit, but the rest is contained within the giant cavern space you have to build your own vault in. For those who are already into settlement building and design, just having this giant space, easily large enough to build a sprawling vault as large as any in the game, is a huge draw for the DLC.
Fallout 4's Vault-Tec Workshop DLC would be more than worth it for most players if all it did was make the cavern space available to build their own vault. That it adds a 4-5 hour quest on top of making these assets available, for the same $5 price as the other workshop DLCs, makes it a really fantastic value, and one that will give a far greater return to anyone who's wanted to take their experience from Fallout Shelter to the main game. But if you're the type of player who expects a fuller story-based DLC from the Fallout series, this may not be for you.