The merged spellbook for arcane casters is fantastic.
spoiler
My last lich playthrough was as undead bloodline sorc. There's a lich spell that raises enemies killed while under its effect, but they can't follow you into the world map.
It's really useful in the longer dungeons but was a complete mess in act 4, since every part of that except the camp and the final dungeon are one location. I was raising every large enemy I killed. After clearing out the flesh markets, I had a large enough blob that they could do all the killing for me with occasional negative energy healing from Staunton.
Ugh, the BOS and Dogmeat are in this for some reason?
Fallout is at this point so obsessed with nostalgia fanservice that I'm surprised Bethesda doesn't just release a Fallout that has you walk down a straight corridor while characters and factions from past games pop out at you.
Maybe the Enclave will even show up again.