Borderlands had a rubbish story to the point where you just didn't follow it. Quests were very MMO esque; collect 10 of this, kill him or kill 20 of these. What made it fun to play was the silly nature of it all topped off by the crazy loot system of near infinite variations of guns. The locations were so-so; the cartoony look and vibe made the otherwise bland environment look nice, and the music was suited to the game. Shooting felt good, as did the various killshots with different weapon types. Playing this co-op is adivised though, it's very much built around a co-op experience and playing alone would get very tedious and very boring.
Play this if you want a lengthy co-op shooter. Don't play this if you play games alone.