Greenlight wasn't an effort for Steam to become an open marketplace. It was specifically an effort to unclog their submission pipeline (which was previously being handled by a handful of employees). Now, these employees can pay attention to the top % of submissions and ignore the crowd-designated chaff.

In that respect, it's working marvelously well.

And it's working even better with the $100 fee, since developers are already stepping up to the plate and offering to individually (!) vet submissions to loan them the $100: http://www.dejobaan.com/greenlight100/

Sure, Steam isn't an open marketplace, but I don't think that was ever really the point. You can just download a program outside of steam or use a competing store - Steam is more like a Retail Shop where there is a bar to get in to keep the quality up.

Steam is never going to be an open marketplace because of its nature, so stop holding your breath.

It is still open marketplace.