I had fun with the building mechanic, but it couldn't make up for the fact that this game is almost completely devoid of main cities to explore. There's Diamond City, which I felt was well made, and Goodneighbor, which was pitifully small. The old games had settlements that were not just larger, but more numerous.
The following cities had many questlines, unique NPC's, and shops, as well as being relatively large.
Fallout 3- Megaton, Rivet City, Tenpenny Tower, Underworld
New Vegas- Goodsprings, Novac, Westside, Freeside, New Vegas
Fallout 4 has twice as many overall locations but only half of the cities, with one of them being particularly small. I blame the settlement system because so much land was allocated to them. In the entire low level section of the map, there's nothing present except ramshackle settlements with generic "Settler" NPCs. This was incredibly bad design and made the early game very boring. The settlement system was fun, but it shouldn't be implemented at the expense of cities and unique NPC's to talk to.