Borderlands is a game I've played for literally hundreds of hours. For me, there is no mystery to it. There is nothing left to discover (I could, of course, be wrong - that's the tricky part of mystery). Everything I see, I've seen before, often as much as a dozen times.
And yet, it's been years since I last played Borderlands, so many of my memories do not instantaneously leap to mind, and some of the ones that do are less than accurate. So, it's kind of like I'm playing the game through the mental equivalent of a pair of heavy gloves. There is a noticeable disconnect between my immediate sensory awareness of the game and my deeper intellectual perception of it.
It feels like my hands are playing the game, and my brain is watching it. That's an odd sensation, but not an unpleasant one. As I work my way through the Caustic Caverns or Earl's Junkyard, my mind wanders, and I'm free to think deep thoughts about the important issues of the day or (more realistically) shallow thoughts about what I'm planning on eating for breakfast (frozen enchiladas, in case you're curious). And I never, ever get lost, which if you've been paying attention to these ramblings of mine, you'd know is the video game scenario that above all others demoralizes and disinterests me.
I guess that might make playing Borderlands sound kind of boring. And while I will admit to fantasizing about the more engaging stories of the DLC and Borderlands 2 (not to mention the completely unknown story of the forthcoming Pre-Sequel), I would call my current experience "comfortable." Playing Borderlands is like sitting around with an old friend. We may have nothing new left to say to each other, but our routine works so well, there's really not a need.