Borderlands has it's ups and downs and the downs are what make it Boringlands...
The Good:
Very fun playability in co-op and interesting story line. The interesting way of using graphical detail and camera styles makes the game almost one of a kind.
The Bad:
This game loses a lot of it's entertainment value when you play it by yourself and you almost find yourself getting bored after a few hours. Personally, I tried playing this game through by myself and also found a lot of problems killing things even though I did most of the other quests to level up. Also the story takes you to a climax where you expect something great and get something not so great at the end. Vehicles get stuck on random things (even though some places have been fixed) and also your character can get stuck in small spot (Personal experience).
In Conclusion-
Most people will definitely enjoy this game if it's played with others but don't expect a really great story because most of the time you will wonder where it is. I think 8.5 is a good score for this game because it gives you 85 percent of what you want and then 15 percent of things that you really do not want.
I can mostly say rent this game before you buy it to see if it really is for you.