In the top 30 critically acclaimed Xbox 360 games, seven weren't shipped on disk. In other cases, such as "Portal," the game was included as a small offering in a larger package. "Braid" presented a Celtic take on Mario and a world in which death did not exist. "Shadow Complex" is a graphically stunning revival of classic Metroid games. "Flower" presented a beautiful and soothing gameplay about a flower dreaming of a life as the wind. Each of these games would be a hard sell to a publisher, to retail chains, and to a gaming audience. But by existing only thorough digital delivery, they can succeed without a large marketing budget or upfront costs, purely by word of mouth.
In the case of these games, a small studio with a handful of employees can create a game that receives press and reviews on par with games that had a thousand bodies working on them. Sales won't always match up due to the nature of the audiences and distribution pathways, but the ROI can be in the favor of independent games.
Looking at the rise of Xbox LIVE and PSN games, I think it's time marketers reevaluate the proposal of advergaming. Doritos is still doing some work in this space, but I think a more organized and produced approach could see success as well. UGC is a great tactic when the market is still maturing, but based on the titles I've seen recently from digitally based game markets, this space is ripe.
By this time next year, I'd love to have seen a CPG brand launch an advergame in Xbox LIVE or the PSN which gets a metacritic score of 80 or above and uses retail distributed codes for DLC. This could just be a pipe dream, but if a brand was willing to step up to the plate, I believe it'd be a home run.