1. Pre-order instead of thumbs up
The current system of thumbs up is meaningless, it's easy to get someone to follow a twitter link to a webpage and click thumbs up. Instead users should commit something like $5 towards a pre-order if they want to see a game on Steam, it would make votes more meaningful and would also give a better indicator of which games will do well.
2. Allow demos that can be played in Steam
This voting system is supposedly to find the best games, but currently it rewards the best videos, descriptions and screenshots. If developers could upload demos that could be played through Steam it would help the best games rise to the top.
3. Curate your damn website
Valve is making billions off of Steam, yet their answer to too many fake/offensive submissions is to charge indie developers $100? How about hiring someone to actually look at the submissions? A simpler way of solving that problem would be to require the account has purchased a game, if it's a fake/offensive submission then they lose that account.
Instead of taking the 10 or 20 games with the most votes there should be some people at Valve actually looking at the games, playing them, seeing how far they are from release. Right now when I see 20 games have been approved through Greenlight I ignore it because I have no idea how close to release they are. I also don't really care which developers have won the social media contest that is Greenlight currently.