Be the change you want to see. Go make the reviews you think should exist if you have a problem with the ones currently existing instead of just complaining about them.
Frankly, people make reviews because they want to share feedback about the game and give encouragement to the creator. There is nothing wrong with that and reviews should be accessible for anyone who wants to write them as long as they meet the minimum standards. We don't get enough of them on the site that we can just say 'only write reviews if the game is complete' and besides, that makes them worse than useless, basically just becoming pats on the back.
And what of those games that aren't great and are complete but set at 2 stars because they're not good? Should the reviews they receive be only summations of the game and not give feedback? Then what makes them different from the reviews for demos if they're doing the same thing? Nothing. They just need a way to be marked as 'old' when an update that fixes the issues mentioned is added.
Honestly, I think our system is pretty good, bar one or two points that we're already looking at.