More shit to shoot? How about dragons?
If you're simply looking for more Borderlands 2 then "Tiny Tina's Assault on Dragon Keep" will do just fine. In fact, even just based on content it's the best expansion for the game by far. Its main quest line spans three lengthy chapters through orc and spider-infested woods, dwarven slave mines and a sorcerer's gigantic tower. The campaign and most of the side quests (not even counting the ones you get once the main quest is done) take several hours to complete.
And this is no re-hash of past environments or themes. You'll find no re-skinned bandits (like the pirates in "Captain Scarlet and Her Pirate's Booty") here. There are dozens of new enemy types, some of which exhibit fairly unique behaviors. Fairies fly around the forest; if you catch them, they give you short-lived stat buffs, but you can also try to fight them. Skeletons and knights come in all varieties, from hulking badasses to conjurors that warp around shooting fire or lightning at you. Necromancers raise corpses to fight for them. Some enemies keep getting back up until you knock them down and pull the enchanted swords from their backs.
You'll see familiar faces, but everything has been reworked to fit the tongue-in-cheek fantasy theme of Tina's Bunkers & Badasses game. Moxxi runs a tavern with rowdy patrons who spurt truly inspired pick-up lines ("I'm surprised you're not orange because that body is legendary!"). New types of chests allow you to roll a die (or two, for some precious Eridium) for better loot. "Shrines" scattered around provide bonuses to defense, speed or ammo for more Eridium. Even all the music is brand new, perfectly fitting with the fantasy motif while remaining true to Borderlands.
In fact, that sums up "Dragon Keep" perfectly: this world could almost have been pulled straight from Fable. It references everything from Game of Thrones to Star Trek, Dark Souls, Doctor Who and Skyrim, but it's still Borderlands right to its dual-wielding, face-exploding core.