The classic that everything looter-shooter gets compared to. Borderlands 2 takes everything from the first game and quadruples it, if not more.
From the Steam page:
A new era of shoot and loot is about to begin. Play as one of four new vault hunters facing off against a massive new world of creatures, psychos and the evil mastermind, Handsome Jack. Make new friends, arm them with a bazillion weapons and fight alongside them in 4 player co-op on a relentless quest for revenge and redemption across the undiscovered and unpredictable living planet.
- All-New Characters and All-New Classes: Four all new playable classes including the Siren, the Commando, the Gunzerker and the Assassin. Step into the role of the Gunzerker, whose highly deadly skills allow him to dual-wield any two weapons found in the game. Not only that, you will build on that skill to do more things with two guns than you ever imagined possible. Dual machine guns? Cool. Dual rocket launchers? Of course! Dual Sniper Rifles? Sure, if that’s your thing! Want to try other styles? More tactical perhaps? There are multiple classes to choose from!
- Dynamic Co-op online, and LAN: Share your adventures with friends both online and via LAN. Borderlands 2 features a seamless system enabling you to drop in and drop out of a campaign without ever having to restart the game. On top of that you can even take your new gear from any game to any other!
- World Connected Story: Find yourself left for dead in the frozen tundra of Pandora as you begin your quest of revenge and redemption. Expose the evil surrounding the Hyperion Corporation and take on the perpetrator of a universe-wide grand deception -- the nefarious Hyperion CEO, Handsome Jack. (Oh, also: he's stolen credit for the opening of the Vault.)
- 87 Bazillion...Everything: In addition to the new gun system, you will lust after procedurally generated shields, grenades, Relics, class mods and much, much more. And you thought the original Borderlands had a ton of loot!
- Brand new environments on Pandora: Hunt through entirely brand new areas of Pandora that are more alive than ever! From the arctic tundra, through the dangerous grasslands, past the mysterious corrosive caverns to beyond, you’ll be surprised by the unpredictable world of Pandora at every turn!
- Brand new enemies: A whole slew of new enemies are out there to kill you in Borderlands 2. Hulking, gorilla-like Bullymongs, vicious predatory Stalkers and the Hyperion mechanical army, run by Handsome Jack, are just some of the new enemies in Borderlands 2.