I really liked Borderlands for the time it lasted for me, it was addicting, but that was when I was playing it off-line for the first time. I beat it twice, on each Playthrough, and reached Level 50 with Siren, that was before the DLCs were released, so after beating it a second time I found myself at an impasse, there was nothing left to do (I had completed all side-quests), and since the game is barely randomized (outside of the loot) then most of it was quite predictable, especially the enemy spawning areas which are always the same, so you eventually know by heart where you need to go if you want to fight, and you know where not to go if you just want to "rush" everything (but that ain't fun, I'm just saying it's possible).
What really put the last nail to the coffin for me with Borderlands is the horrible on-line games management, there's absolutely no way to filter and set host-side rules to the games I host, I cannot control the minimum or maximum ping of the players who join my game, I cannot perma-ban them if they are troublesome (and curiously there's lots of immature kids... or worse, immature adults playing Borderlands on PC, not sure why) so it's exactly like Left 4 Dead, you really need to play with friends to have fun with this on-line. But I haven't played it ever since I stopped, which was before the DLCs were released, and I do not know if one of or both DLCs added new on-line features and ways for a host to set game rules, but even if it did I don't think I'd bother buying any of them since I for one don't know enough people on Steam who play this, or who play it at least regularly.
But despite all of that I really did have lots of fun with it for the time it lasted, and it certainly was very addictive. With that said I won't play it again for a couple of months until I don't remember anything about the story-line and have to start it again eventually to refresh my memories about it. But for those who do have friends who play it often enough and who are mature enough to play it then I could surely understand why and how Borderlands can be fun, it just ain't the case for me, and I think it's a shame to be honest, the raw potential behind Borderlands is just mind-blowing, it just sadly wasn't exploited at its fullest.