Bounty of Blood is a fairly traditional story-based DLC, so don't expect sweeping changes to how Borderlands 3 plays. You'll run through some new areas, a few mountainous, some more arid and flat—all evocative of the wild frontier of the American Old West.
In a play that I truly dig, it was revealed during the stream that an omniscient character will narrate the whole adventure. Seeing that Borderlands 2's best DLC, Tiny Tina's Assault on Dragon Keep, followed a similar structure, maybe we'll see Borderlands 3 break the fourth wall in some clever, genre-tinged ways.
It looks like more Borderlands 3, which I didn't like much when I reviewed it last year, so you probably already know if it'll be for you or not when it releases on June 25.