Borderlands is an RPG-based First Person Shooter set in a postapocalyptic wasteland. However, the seemingly promising combination of genres doesn't result in a particularly fun game.
In Borderlands, you play as one of four characters - the hunter, Mordecai, the siren, Lilith, the soldier, Roland, or the berserker, Brick. Each has his or her own special abilities, and basically serve as the game's classes. Mordecai can use his pet bird to attack enemies, Lilith can turn invisible and apply elemental damage to weapons, Roland can deploy a sentry turret with upgradable weapons and bonuses, and Brick relies mostly on his brute strength and power. At the beginning of the game, you pick one of these four; as the game goes on, you can level up certain abilities, which serves as the game's only real stab at customization. You can also change the colors of your character model, but the characters' costumes are so quirky and wacky that it still never really feels like "your" character - just like you've painted someone else's character.
The game's main draw is the wide range of weapons, which includes the usual mix of pistols, rifles, SMGs, and shotguns. However, individual weapons can have different bonuses and penalties - damage, ammo capacity, scope range, bonus effects like fire or acid, and so on. This is meant to be the game's "RPG" element. However, rather than being an interesting way to carry out different missions, each gun basically has you do the same "backpedal and shoot" tactic no matter what you do. There's no variety in the weapons - just in how long it takes before something falls down while you shoot at it.
The grenades are a little better, but not much. Rather than getting different actual grenades, you get equipped with an item that turns your grenades into different grenades. These include sticky grenades, bouncing grenades, and teleporting grenades. Even these, though, are just regular grenades, in FPS terms. There's nothing that actually changes the way you play the game.
As far as gameplay goes, it's basically Diablo or World of Warcraft, except with guns. Shoot things, level up, shoot higher-level things, level up, shoot even higher-level things, level up. In addition to your guns' damage, your actual character somehow does more damage per shot by leveling up. This would make sense with, say, swords, which are driven by strength, but with guns it's just kind of dumb. The game's bizarre attempt to be an RPG is really just kind of annoying - it boils down to how much damage you do per shot to things of various levels. Things far lower-level than you can't really hurt you even if they get the drop on you, while things higher-level than you just need to hit you once with their normal patterns. Things don't get "more difficult", they just have bigger numbers. The entire game is basically a cycle with no appreciable gameplay differences, apart from the skills you buy. The game is, on the whole, motivated by quests, like any other RPG, but they just serve as periodic rewards to move the game along, since it's not like you can go around not doing quests - they're the things that open up new areas.
The game's other main draw is co-op, which is at least a reasonably good idea. However, it's difficult to say that it's a good game because of co-op - rather, the co-op feels kind of irritating, because you have to be at a similar level to your co-op comrades to get anything done. It's usually best to start a bunch of new characters all at the same time so everyone's the same level, but that's also really annoying. Co-op is much more frantic than single-player, and it's harder to maintain the simple "dodge attacks, shoot enemy" gameplay when there's four people and the enemies are going for all of them. There are some bits that are made more fun with multiple people (like the usual Halo-style jeeps with a driver and gunner) but these are few and far between.
On the whole, playing Borderlands was more of an annoyance than anything. The guns aren't responsive enough to be fun, the screen is often crowded by the heads-up display (especially in multiplayer), and despite the tight, linear maps, you're required to go back and forth to places to turn in quests. The cel-shaded graphics are kind of neat, and the gun sounds are pretty good, but mostly everything in the game is bland and basically a huge grind. If you're willing to subject yourself to huge amounts of grinding for no real gain, then you might be fine with Borderlands. However, for either casual players who want to move through things quickly, or hardcore players who want to actually get some results for their skills, Borderlands isn't a particularly great game.