The new world and the campaign are the main draws, but you’ll also see a host of new weapons, mods and cosmetics.
Guns, Love and Tentacles is included in either the Super Deluxe Edition of Borderlands 3 or the Season Pass, but you can also buy it separately for $15 if you’re only interested in this expansion. You don’t need to have played the main storyline to get started, though. You’ll need to have access to the starship Sanctuary III if you want to use an existing character, but you can also create a new persona and bypass the opening of the primary story to get straight to the new material. With that said, it’s probably worth playing through at least some of the core story first. These characters have significant history (including in B2 for Hammerlock), and it’ll make more sense to dive in once you understand their backgrounds.