@Monogram
You do get a lot of repeatable settlement defense quests but I believe there's something like 50 quests that make up the main quest. Every companion has their own quest, notably Piper and Strong have two. And then each Faction has their own series of quest chains depending on factors such as Charisma, Favor with the Faction, and so on, could be another 50+ between them.
Then there are also a lot of random in-world quests that you'll pick up out of no where from just wandering around. An example of this is the awkward escort quest for Billy the Ghoul. Or the two, possibly three, for Pickman.
Also. You can get the best melee weapon in the game by killing the behemoth in Swan Lake.