An interesting twist on the RPG genre, though it may not be the most original attempt, it is one of the best.
The graphics are very interesting. An almost cartoonish style while still retaining detail and realism. While some areas such as buildings are lacking graphically, players and NPCs all look impressive. The guns look pretty cool, and come in a variety of colors/appearances.
Humor, often a miss on games. Borderlands wants you to laugh, and unlike most games where you end up laughing at them, Borderlands encourages you to laugh with them. While still keeping it relevant to the story, Borderlands puts humor as one of their top priorities on game design. You'll probably grin or chuckle at at least one of the gags. While having humor in dialogue, even some of the missions contain some crude humor such as "collecting panties".
Gameplay, like I said, this isn't the most original gameplay ever, but it definitely doesn't feel exactly like another game. While giving the player powerups, character abilities, character skills, etc, etc. Borderlands maintains a fun, and creative gameplay style. Not only is it addicting, it can easily turn into mindless fun. There isn't much that is specific to say about the gameplay, it's not the most original style, but it's definitely a fun one. My biggest issue is with the "checkpoint" system. I would prefer being able to save anywhere, and being able to respawn as I chose too, as there are few things more frustrating than getting stuck in a poorly designed area then not being able to restart at your checkpoint because you cannot die.
All in all, Borderlands is one of the best games I've played in a while. It's definitely worth a rental if not a buy. The multiplayer is fun, the single player is fun, and it's a long and thoroughly enjoyable experience.