I've noticed that I apparently tend to review games in blocks of genres. Last month, it was superhero games. This week, with Torchlight and Borderlands, it's Diablo-style gameplay. Oh, there's no mistaking it - though Borderlands has all the trappings and game elements of your standard FPS, it's the Diablo style through and through; where your primary motivation is not fame or fortune or revenge but loot - lots and lots of loot.
In a way, that's the goal of the game's flimsy story, though: On the wasteland planet of Pandora, there are rumors about a legendary Vault filled with treasure and alien artifacts. Your character has heard the rumors and is out to prove them true. And as your character searches for the shiniest guns in the galaxy, so do you. Gearbox Studios has made quite the deal over how its procedural generation results in literally millions of potential weapons one can acquire, and it's true - there are lots and lots of guns (and other equipment) in the game.
Borderlands' uncanny arsenal is probably its greatest strength, because it goes so very far beyond the standard ritual of FPS games: "Oh, a shotgun. Oh, a bigger shotgun." In Borderlands, it's "Oh, a shotgun. Oh, a bigger shotgun that shoots explosions." You get guns that shoot fire, lightning (haven't seen any shurikens yet, though), and acid. You get guns that shoot other guns. You get grenades that teleport to their destination, grenades that split into smaller grenades, grenades that explode on proximity, or grenades that do all of the above.
It isn't just that you get shiny types of ammunition, though. Every time you get a gun, you need to weigh its positives and negatives against your current arsenal: This submachine gun doesn't do as much damage as my current one, but it has a larger clip, shoots faster, and does extra damage in melee - is it worth taking? It can be hard to discard a faithful weapon that has served you well when you get something more awesome, but the shoot-loot-and-boot gameplay works well.
It had better work well, because everything in the world of Pandora is trying to kill you. Bandits and wild animals all want your flesh, and there's a wide enough variety of randomly-generated enemy types to keep you entertained (and on your toes). Each of the game's four classes has their own tools to keep themselves alive: The Soldier can throw down a sentry turret that heals, replenishes, and guns down anything nearby, the long-range Hunter sends his pet bird of prey in to peck out some eyeballs, the stealthy Siren can turn invisible as either an ambush or escape tool, and "Brick" charges into melee and pounds things to dust, Incredible-Hulk-style.