However, it's probably best that you live your FPS mindset at the door, because Borderlands is also an RPG. Indeed, perhaps it would be prudent to call this an Action RPG with guns.
The thing even the most seasoned FPS players will be dismayed to learn is that, no matter how quick your reflexes are, you'll still find yourself beating a hasty retreat to enemies who are above your level. Though you do have to aim, of course, it's more just to save bullets than anything else. This is more an RPG with shooter elements, rather than a shooter with RPG elements. That said, the game only offers a core RPG experience, instead making an attempt to balance elements of the two genres.
The game hits the ground running, introducing you to the four classes, while running you through various aspects of the gameplay. The four classes are the Brick (A melee-oriented berserker), Siren (A sassy young woman who has a preference for elemental weapons), Hunter (A sniper with a pet attack hawk), and Soldier (A veteran who has ample medic and support abilities). Each class has its own unique ability and skill tree, and also has preferences for one weapon type or another, granting damage bonuses when a gun of that type is equipped. For example, the Soldier can deploy a turret that not only defends him, but provides decent cover. His skill tree features such perks as having the turret continually restock any allies nearby, or giving his shots healing capabilities (like the Medic's Phoenix weapon in Resistance 2).
Borderlands also features a loot system that Diablo players will be right at home with. The game's engine randomly generates weapons from various parts, colors, and ammo types, meaning there are essentially hundreds of thousands of weapons in the game. You could come across a shotgun with a scope, a pistol that shoots rockets, a submachine gun with incendiary properties, the possibilities are limitless. But since, even with inventory upgrades, you can't carry more than a couple dozen items at a time, you'll be swapping weapons and items VERY frequently, to stay on the cutting edge. Weapons you don't need can be sold for a decent price (I'd say besides quests, selling stuff you don't need will be your primary income source).
However, the story is very light for an RPG. The beginning tells the story of a planet known as Pandora, an unfriendly land featuring little more than dust and rocks. However, legend has it that there's a secret hidden on the planet. This secret, known as the Vault, is said to contain everything a person could ever want, from riches to women. Of course this sounds pretty far-fetched, but as you prepare to get off the bus (after choosing your class), an unknown woman appears in your mind, claiming that the Vault does in fact exist, and encouraging you to seek it out. She continues to pop up periodically throughout the game to offer advice and comment on your journey thus far.
Few of the characters have much of any backstory to speak of, though it's implied in the beginning that the four class characters have been friends since they were children. You arrive on Pandora knowing nothing about it or it's inhabitants; just the legend of the Vault. I think this is a bit of a missed opportunity, but it doesn't seem like the focus of the game was ever on the narrative anyway.
On the HUD you'll find a variety of useful things, including a compass, your level progression meter, and your shield and health meters. Borderlands features a health system much like Halo's (the first one). You have a shield (which, like weapons and other gadgets, is upgradeable and likely will be swapped out frequently) which blocks attacks until it's depleted, at which point your health starts to drop. Your shield will recharge after a few seconds of not being hit, but health usually has to be restored with items. EXP comes from defeating enemies and completing quests. Some will be happy to know that you'll rarely have to grind for XP or even money in Borderlands. Quests give you pretty big chunks of both XP and money for your troubles, and any monsters killed and unneeded weapons sold in between will likely pick up loose ends. As long as you keep a healthy quest log stuffed with active quests, you'll find you're almost always at the right level to continue progressing. And you'll always have something to do, for that matter.
Borderlands also features four player co-op. You can either play locally in two-player splitscreen, or online with three others. The co-op is really fun, but only if each of the players are at or around the same level. While it is possible to boost (MMO term for a veteran player accelerating the level progression of a newer player) lower leveled buddies, until they reach your level, they'll find themselves unable to help much at all in battles, since you'll be hard-pressed to take on enemies more than 2 levels above you (similar to other RPGs). To be frank, comrades that aren't strong enough to help you in battle aren't much more than dead weight.
Overall, Borderlands is also a great-looking game, featuring a cell-shaded graphic engine. Bugs are minimal, and loading times only occur when you first start up the game, and when transporting between regions (yes, regions. Each of which are gigantic, despite the reasonable load time). The engine also handles chaotic situations well. Even in splitscreen the frame rate rarely dips noticeably.
Overall, Borderlands is a great game. More effort could have been put towards the story and characters, and the cooperative play isn't as accessible as I might have liked (though that's to be expected from an RPG). The game is light on both RPG and shooter elements, but retains enough of both to form a really fun experience. Moreover, this is a game with personality, and it really is almost one-of-a-kind. 8.0/10.