A reasonable summary of Dark Souls, there.
The concept of Steam tags should be fairly self-explanatory. You can swing by any game listed in Steam’s store and label it with pretty much any word you choose (though swear words will apparently be “filtered out.”)
I’m having quite a good time with it. I’ve already tagged Alpha Protocol as “underrated” “beard simulator,” X: Rebirth as “broken” “unoptimised” “garbage” and Dark Souls as, of course, “praise the sun!” I was also delighted to find Barbie Dreamhouse Party already tagged with “horror.” The system works.
You can also browse by popular tags, which might actually be helpful if you want to find all the games that allow local co-op, or titles that share a cyberpunk theme or something.
Tags will be written in whatever language you have Steam set to. So, in Valve’s own example, if you have the language set to Danish you’ll see popular tags from other Danish language users.
The FAQ for developers (at the bottom of the tag information page linked to at the start of this article) seems to suggest that there won’t be much recourse against people labelling your game as terrible. “Tags can be a good indicator of when there is a mismatch between how you perceive your game, and how your game is perceived by customers,” it says.
That’s all in good fun for titles that are objectively broken, but maaaay be open to abuse. Gone Home’s dev seems to be taking it in stride though.
