Equally important as the characters are the stages in brawl games like Smash Bros, and of course, PlayStation All-Stars Battle Royale. The way these games exist, though, requires what is essentially a 'mash up' mentality. You're mixing and matching all sorts of franchises in order to have a varied roster and locales.
Battle Royale takes this to the next level by mashing up different worlds, creating creative levels. It's not just a visual thing in the background, because the levels interact with the player in different ways–which become complex depending on what's being mashed up. The developers go into details behind the ideology of the "mash up" in Battle Royale in the video above.
Beyond this, the music in the game reinvents many songs–so you won't be hearing stuff you've heard before. The video is also good for getting a look at the different stages included in the game, some of which I hadn't seen before personally.
The fact that Uncharted 3's level then becomes Bioshock infinite is amazing, and it makes me wonder what else will be mashed up in the game. We'll know come November, when the game launches.