I loved this game for about a month, maybe two of single-player gaming. Then I played a couple of the DLC's. My husband, during Xmas break, tried it out & played it for a month or so as well. He's not a big gamer but he liked the simplicity of it (eg, he's not a story/dialogue person). So we played some co-op together (over our network) and that was a lot of fun too. I haven't had the desire to pick it up again since tho. Will I buy the sequel? Most likely. Do I think the game has a lot of long-term longevity? For me, not really.
And the loot & stat hunting? Just part of the action-rpg loot-based genre. Not everyone does it of course, but they're
designed for that style of play/endgame as an option ... if you're not into it/don't like random co-op games, you just start new characters, try weird new builds, or get into dueling/PvP etc. If the game is designed well, I like and can get very wrapped up into item-hunting. But Borderlands just doesn't have the item set to be interesting enough to motivate me to do it, personally. In Diablo2, if I'd found a legit Zod during one of my runs (never did), I'd have fainted in shock/joy. Borderlands & finding the next dmg. stat-level of the same model orange poison pistol or whatever? Not so much. Some people really like item hunting for elusive stuff/stats tho. But it's not everyone's thing.

I've only ever played it solo and I love it. I was turned off of going online because, from what I've heard, the majority of online players are kids with modded weapons and shields that can corrupt your saves.
Doesn't corrupt them...it overwrites them because (last I knew) the host's game files dictate stuff, and for some reason the game replaces your .ini with their .ini settings. If you set your .ini file (or whatever it was) to read-only, that doesn't happen. eg, if they've altered their file to give them a zillion backpack slots, and you don't want that, just backup the related file or make it read only and you won't get it from them. Don't know about anything else, or if it's changed with some patch.