The current reviews seem to be a little bit unfair. Giving the game a low rating because of buying it from another country isn't really very fair.
When I first bought Borderlands, I got very frustrated because I could not for the life of me get the co-op to work. I bought four copies. One for me, the other three for my friends. Playing co-op with my friends was the whole reason I bought the game in the first place. I then played the game through in single player and had hours upon hours of fun.
After a while, the makers of the game (Gearbox), fixed the co-op issue. This is when the game really came to life. I played through the whole game again, with only one friend. We would play for hours a day, every single day. It was that addictive. Very few games these days keep me coming back for more and more, but so far I have 200 hours logged into Borderlands, and it's charm is far from wearing off on me. I'll soon be playing through it again with three friends.
The graphic style is an interesting one, but personally, I love it. Too many people these days care about graphics and only graphics. Borderlands looks amazing, but more importantly, the gameplay is almost spot on. There are a few tiny flaws, but nothing really worth mentioning. There are four different characters to play as, each one being completely different. They all play differently. Each character also has a "skill tree" which lets you change the play style of your character, depending on where you spend your skill points.
I've played hundreds and hundreds of games in my life, and I rank Borderlands in my top 10 games of all time. I can't quite put my finger on what I like so much about it. Maybe it's the games charm. Maybe it's the graphics style. Maybe it's the humour. Or maybe it's everything combined that makes such an incredible game.
I would definitely recommend this game. Single player is fun, but co-op is definitely where the game shines. If you're on the fence about this game, just go for it. You won't regret it.