Steam Greenlight being how it is partially is a good and bad thing. I think focusing on a few titles and stating, "How did this get through!?," is a sensible and simple/sound argument, but on the flipside, I also don't think it is representative to the whole of the system.
It's obvious Steam is eventually going to become an open market. They have for a long time been implementing systems to promote bigger releases, let users dictate the 'quality' of a game, and finds ways to try and let users find games that may personally interest them. The system is still a bit rough, which is why I think we still have Greenlight and the wall, but the wall has been loosened over time. I think eventually they're just going to put in a system to check if the game has all the legal rights to be sold and doesn't step on either copyright or their service platform terms toes, and if the game can legally be sold and abide by Steam's terms of service, then it can be sold.
This is not overwhelmingly a good or bad thing. There's obvious pros and cons at work here. Firstly, this may be something of a completely new design for any sort of gaming storefront. We're given both the biggest of the big games along with the smallest of the small games, right next to each other. For every Metal Gear Solid or Grand Theft Auto 5, growing Japanese support, and recent triple AAA release, we also have fantastic indie games, darlings, overlooked gems, and enthusiasts projects, as well as crappy shoe-horn games, low quality products... And EVERYTHING in-between.
As a collector and an enthusiast of a genre, this does appeal to me. Especially since I think there's a lot of really good games that go under people's radar. Honestly a lot of hidden gems out there, and we also are living in an age where people are becoming more aware of the creators behind games. If you do shitty practices or release purposely shitty games, that will stick with you. The same is true for the opposite. We're entering an age where individual developers almost have to build a name for themselves if they want to stick out from the crowd.
And honestly? More of what releases is at least decent other than terrible. I'm not saying there isn't hundreds of terrible games on Steam, but I think there's a proportionately larger number of actually quality games already in the marketplace that forms a fiercer competition. I think the key difference to this sort of open market compared to other attempts at an open market for games is with Steam, already every major developer is on-board deep and it has a huge userbase, and there's literally a library of thousands of games already established on the marketplace. You're not going to get very far with some shitty game that no one cares for. The disadvantage is some legitimately good games get swept away with the tide, but it makes a very different 'open market' than we've seen before, that I'm curious to see how it plays out.
I think it's for the better, I think having a place literally any type of game can exist in is both fascinating and opens all sorts of methods to obtain really anything you may want. But before these floodgates are opened, I do think Valve themselves need to do as they're doing, and continue to improve their methods of discovery, visibility, browsing, and general ease of use, and ways to dictate market value for a game with user opinions.