This is a fantastic game. Been playing it on and off ever since it came out.
Me and a friend have finished this game probably 20 times now! Every times a new DLC has come out we've replayed the whole game (well, not with Moxxys Underdome Riot but the other ones) from start to finish + DLC. We started on the 360 but has since then moved to the PC because that offers better gameplay even if I think the 360 works well considering its a FPS, they've made the controls pretty much as good as they come considering.
So what makes me love this game so much?
I love a game that uses random item drops, and I dont mean WoW style "random" (yeah right. bullshit.) drops where the items are scripted and have predetermined values but where the items truly feel random with slight differences. After finishing Borderlands as many times as we have now you notice patterns in the weapons and you can see that the system isnt perfect when you find 2 of the same gun with the same name even tho its not one of the unique weapons. Random drops is the way to go, my love for this system started with Diablo and I dont know why people would use another system.
Another thing I love about this game is the humor and the small subtle things such as the grafitti you can find such as turtles all the way down
I could go on and on but this is truly one of the best, if not the best games of 2009. And I'm not nearly done with the game yet either as me and my friend have another LAN party coming up where we plan to play only this and my Dreamcast in between (Power Stone, Ikaruga).