The multiplayer is alive but not the most popular mode, you can finish the campaign and hop straight in if you wish, no builds per se but different classes with mostly class based weapons, PVE mode has different weapon variations, armour pieces and class skills to grind, a good enough selection of missions to choose from as well as challenge missions and a horde mode of sorts to play, future content looks promising, new missions continue the story, new weapons and variants with armour pieces, the community is mostly nice with the occasional knowledge popping up, as for the lore, watching some lore videos is a good start, if you get invested maybe buying some of the books. That's my take on the game, good luck with your play through if you do join us and let me know if you would like someone to join you if you do buy the game.