Borderlands is an addictive RPG FPS loot hunter. Its light on story, big on flavor, and above all, just plain fun.
The guns are the heart of Borderlands, pure and simple. Borderlands sports a huge weapons creation engine, so nearly every gun is unique. Weapons are divided into the usual categories, Snipers, Pistols, Rocket Launchers, etc etc. Not only do the stats change between guns (accuracy, fire rate, damage, etc), but guns have extra effects, from bonus melee damage to the common and often powerful elemental effect guns, to Legendary "Red Text" guns, that have a caption (such as "Unending Firepower") that gives an effect (such as ammo regeneration). While you loot bodies, weapons chests and piles of muck primarily for guns, they aren't the only loot in Borderlands. Grenade mods (equipment that make your grenades have special effects), Shields, ammo, extra health, and money also drop. You spend a lot of time in Borderlands opening things and picking stuff up, but thats the fun. Its satisfying finally finding a new and better gun or a sweet shield, and any spare guns you can sell for money at a local gun or ammo vending machine. Ammo shortages do occur, especially earlier on, but the ammo is handled well enough that while it often feels like your nearly out, just enough ammo will drop to let you keep going.
Borderlands world is funny and memorable, especially the helpful Claptrap robots that help you out, as well as certain characters like a crazy scientist. That being said, this game isnt heavy on plot. The ending is fairly unsatisfying, and when it tells you to "search" for something, it is actually shown right on your map. This is great for people who want loot hunting and shooting in a memorable world. If your looking for more traditional RPG elements, such as dialogue, story, or your decisions playing a role, then Borderlands might not be for you.
Borderlands looks and sounds great, but some people won't necesarily like the graphics. Borderlands isnt a "realistic" graphics game like MW2. Borderlands is more cartoonish. which fits well with its over the top ridiculousness. Realistic graphics simply wouldn't work for this game. But while the open environments are often similarly dusty, its a detailed and beautiful world (in its own, beat up way).
The four classes in Borderlands are great. They each have a unique action skill and skill trees. They are all viable, which isn't surprising as Borderlands in general isn't a particularly hard game. A few boss fights can be rough, but most boss fights are fast and easy or long and slow. The bosses are hit or miss, some are excellent and memorable, some quickly fade away as just another big guy.
Borderlands works excellently for co op and single player. Co op can be split screen or online (up to four players). You can complete quests together, and the monsters get tougher as more players join, just as the loot drops get better.
Borderlands has some flaws however, but they mostly get expressed near the end of the game. Borderlands is a long enough game to feel satisfying, and you can playthrough the game again, keeping your character. This option is great, the first playthrough will get you through about level 33, and you can reset all the quests, while keeping your guy, and all the quests scale up to your level. After the second playthrough, all enemies and chests scale to level 50. While it is pretty long, Borderlands end game has its flaws. Money, toward the beginning of the second playthrough, loses all value (and it was already not worth much to start with). First playthrough there are weapons and shields to buy in vending machines, but at playthrough 2.5, a single 3 minute run around New Haven, reselling every gun will net you well over two million dollars. The max money you can have is 10 million. Money isnt worth anything when you can easily max out your money in 10 minutes.
Borderlands multiplayer is great, but the PvP is lacking. You can duel, to see whether you or your friend hass the more badass guy, but dueling isn't particularly satisfying. It tends to be over quickly, and each class feels over powered in duels in some way, so duels tend to be less skill and strategy and more a few seconds of holding down the trigger. There are also arenas, but those tend to suffer similar problems. Borderlands is really about killing mobs and getting loot. While you can go back and rekill most bosses, and go to your favorite area and farm more items, at the end of the game there isnt much that your farming for, which is a shame.
Overall, Borderlands is a fun loot hunting shooter that is worth your money, just don't expect it to be a realistic MP shooter like Halo or CoD