Leaving aside the fact that all this conversation is secondary to mankind's supreme overlord and true god: Money.
I dont think its a great idea. Have you talked to other gamers? They have the shittiest opinions. Some guys on this site for instance think FFX is the best in the franchise. Wild. Just look at Metacritic's user reviews. They are garbage. Kids go from 0 to 10 for the dumbest of reasons - mostly just for the sake of trolling. Even if you were to link it to achievements to prove they've played the game, I doubt much would change. However condescending this may sound, Its very hard not to dismiss these people as immature kids, the less voice they have on the industry the better. I cant imagine devs looking at this sort of app and taking the comments seriously. How do you filter the legit good feedback from the sea of garbage?
I'd question that devs "cater to journalists", but thats a conversation for a different thread. Seems to me that you are giving "professional" reviewers more importance than they really have. The thing about them is that at least they have to justify their shitty opinions, if they get a shitty rep, people stop caring about them, stop reading them, sites eventually stop considering them in their lists, and its a problem to them because its their job. Theres at least some degree of consequence.
