Enter the madness
Borderlands is a game that promised to merge the FPS and RPG genres, and it's success is largely due to the fact that the developers didn't allow the use of either genre to reduce the effectiveness of the other. While in other games one may outweigh the other, such as Fallout 3's robust RPG elements, Borderlands really shines because of the level of balance that exists between its two halves. Really, there are so many good things about Borderlands that, when its performing at it's best, there is really nothing quite like it. This in large part is due to the cooperative mode that allows up to 4 players to ravage the wasteland at once. Really though, most everything about this game is really tight - it controls well, there are bazillions of weapons/shields/grenades/class mods to be found, and the 4 playable classes are really diverse and interesting, and each contains multiple build options, making a group of people playing the same class totally valid.
There are, unfortunately, some hitches that keep this game from being truly of legendary quality. The real focus seems to be on playing cooperatively, so playing by yourself can sometimes become extremely uninteresting. There are also just a number of strange things - not game breaking by any means, but strange, and often annoying - such as the fact that sometimes guns that are exact copies of each other sell for hugely different amounts, and even sometimes guns that are strictly better than another will sell for less. Also, if you go for a second playthrough, which levels all the enemies up, you'll quickly notice that your vehicles are exactly the same as they were in playthrough 1, meaning that they'll blow up after only a couple hits. Mostly these kinds of things are only annoying because they make you stop and think "......huh?", but they are annoying nonetheless. My only other real complaint is that while money plays an important role at the beginning of the game, before making it even halfway through one playthrough it will be a completely obsolete part of your experience, because you'll quickly surpass an amount you could ever spend. I'm also not going to talk about the story, because it was pretty bland, but honestly, I didn't give a crap so it's not really a complaint for me.
These (mostly) small issues aside, Borderlands is a really enjoyable game, especially with friends. If you like shooters and don't outright hate RPGs, you'll probably enjoy this, and if you like digging for loot (ex: Diablo) and gaining levels, you will also most likely enjoy Borderlands. I'm really hopeful for the potential for DLC expansion, as well as a sequel, because Borderlands really has the right stuff for a successful, epic franchise.