I thought Borderlands had a lot of potential, but ultimately failed because of all the psychological ploys they packed into the game to keep people playing. Obviously this is an unpopular opinion, though, judging from the sales numbers.
I hate any game that doesn't give me my experience reward right away when I finish a quest. I killed the enemies, I got the thing, I freed the girl, and I should not have to go back and "turn in" my quest to get anything but the money and/or item. I also hated going back and forth doing quests for the same people over and over. Every person seemed to have an endless list of stuff for me to do and by the time I got to the bottom of it I was ready to use some of the guns I had picked up to take the quest giver out in a blaze of glory. Going back and forth like that is an addiction strategy used by MMO's to make you turn in a quest and then immediately afterwords see the little "quest available" exclamation point on top of someone's head so that you say to yourself "ok, just one more quest". Knowing this and seeing it in a game like this (a third-person shooter rpg) just kind of rubbed me the wrong way.
I suppose Borderlands is also all about the multiplayer, which I didn't indulge much in. I suppose it could be argued that I didn't get the full experience then, and that may be true, but single player should still at least provide some entertainment value.
I did, however, really like all the different guns and their strange elemental effects. Finding a really cool gun with an extra lightning damage modifier always made my heart flutter. But it was always a hard decision when I found a better gun without the cool lightening effect on it.
