I don't mind the graphics at all actually, but wherever art is any good or not is subjective. I suspect the rationale was that they wanted an art-style that wasn't 50 shades of brown, and a vaguely cartoonish style compliments the general retro-future the game goes for.
It's a good game overall, but the bone I have to pick with the game is that how you're forced to choose sides at inconvenient times which ruins the immersion and you end up failing a load of quests because of it. There should be more story-line paths really.