XIII (2003) had done the cel-shaded look before TF2 (2007).
Yes, but it didn't have goofy looking, cartoon-proportioned characters, as in TF2 and Bordlerlands. Plus XIII had very crisp imagery to match its comic book style. Borderlands feels like it only has cell-shading because it would look crap compared to its peers if it had a more realism-inspired look (relatively low-poly models, bland and low-res textures, etc.).
I hope there's more to
Borderlands than "loot-whoring" and "mad-gunning." Based on the killing and moving on argument we could say
Serious Sam is more like
Diablo than most shooters, minus loot and experience, since it's entirely about killing hordes. Or how about
Left 4 Dead? They're both playable in singleplayer but that's more for testing purposes than anything else, the core of these games is multiplayer. Is that how I'm supposed to think of
Borderlands? As a purely multiplayer experience?
I just assume most people play singleplayer for the story and multiplayer solely for the gameplay. That said, I do generally play way more singleplayer than multi. I just hope
Bordlerands will not be boring as a singleplayer game, usually story covers that fairly well.
I thought
Bioshock had a good storytelling convention, with the audio logs and journals scattered about. It made the story available for those who wanted to look for it but not in the way for people who just wanted to gun it.