Humor, character building, and guns. Lots of guns.
I've been following Borderlands since it's unveil back in September 2007. Since then, it's been clear from the start what kind of game this was going to be. Sure, the art style changed, but Gearbox has delievered a product that does exactly what they said it would.
In Borderlands, the player chooses one of 4 characters. There is a Siren, a Berserker, a Hunter, and a Soldier character. All 4 characters have a unique action skill that is gained at level 5, and from there the similarities between two characters of the same class end. Thanks to a very well implemented experience system, the player can spend a point in their characters skill tree, which has 3 branching paths. Each path offers a much different gameplay experience, and helps provide replayability as well as character specialization. For example, the Soldier can max out his Infantry tree, which will increase his damage with various weapon types, increase reload speeds, provide bonuses to stats for a few seconds after killing an enemy, and eventually let his action skill, a turret, fire rockets as well as bullets. On the other hand, players who follow the Medic tree will be able to heal teammates by shooting them, increase their maximum health, regenerate the health of players within the radius of their turret, and revive teammates faster. Without going into that much detail, this diversity carries over to the other 3 characters, where the Siren can be built as a Rogue style of character, a mage, or a combination of the two, the Berserker can be built as a Tank, a Melee fighter, or a Grenadier, and the Hunter can be built to utilize his pet Bloodhawk to maximum effect, or snipe with incredible efficiency, or even be a pistolero.
Gameplay boils down to finding quests from either a person or a bulletin board, following the objective marker, killing anything in your way, grabbing any cool guns the enemies drop, and then turning in the quest after the objective has been met. Thanks to a large selection of quest types, it never becomes monotonous. Yes, there are a lot of "Go here, kill 50 of these guys", but the player will always jump at the chance to do so, if only to see what guns will drop and to further build their character. One of my favorite quests was actually rather 3 quests all in the same area. I first drove a vehicle out to a hive of flying bird type enemies, called Rakks, and gunned down 10 of them with the vehicles machine gun. That task accomplished, I drove down towards the bandit's who had made the windmill facility their home, ran over a few of their buddies, got out and shotgunned a level 8 midget shotgunner while a Badass Psycho ran at me on fire, and so forth. That long fight over, I then went into the facility to grab a note with the location of the Mine Key, then went outside and turned on 3 of the windmills. My jobs done, I drove back and turned them in for my hefty XP reward and a few new toys.
By constantly rewarding the player, Borderlands keeps them playing for hours on end. My first sitting alone I played for about 7 hours, and I would say I had seen only an eigth of what the game had to offer after that time. The game truly is a BIG package.
The Co-op is a blast, allowing four players to work together online. You can also bring a second player in for local split screen. In co-op, the enemies are simply thrown out in larger numbers, but it works. The only real problem is there is no trade system, and no rolling for items. In other words, if someone joins your game, there is nothing stopping him from grabbing all the loot. This is dissapointing, and really limits the amount of time you'll spend in co-op, because you'll only want to play with some good friends. As for the lack of trading, if you want to give someone something, your only option is to drop it and hope they pick it up instead of someone else, again reinforcing the reason why you would be better off playing with buddies.
The graphics aren't beautiful, but they are VERY pleasing to the eye. They do suffer from the unfortunate blur problems many modern games do, but after about 10 seconds everything will look like it should, and it seems to stay that way for the rest of your play session.
As I said earlier, the co-op is where the problems in this game are seen, but there is also an issue in the game itself. I wouldn't say it's a problem, but it's a little dissapointing.
I'd say that in my time with the game, my first 20 levels were spent fighting either bandits or Slags, which are like mutant wolf dog things. That's fine and all, and the game did provide plenty of variants of the two types of enemies, but it'd have been nice to see more diversity earlier on.
In the end, Borderlands is my current choice for Game Of The Year, and I HIGHLY suggest you purchase this game. Randy Pitchford and his team have made exactly what they said they were. And it's damn good fun.