Oh, they do boost games, but this is not tag specific. They boost new games. The popular ranking inlcudes a little boost for new games. But I do not know how much or how long. They want to mix up the ranking a bit, so people would not always just click on the top games and thus the ranking never changes, imho. So popular is actually new & popular, but with a lot less emphasis on new.
And of course, the featured list. Those are hand picked. But I do not know how big that boost would be, by having a game on that list. Someone on that list would have to disclose analytics. It should show, if people visit the game from that list or from a regular tag list.
Likewise for the horror games mentioned here. The analytics should tell, if the link was from youtube, should it not? Or are those referals hidden? At least it should show, if the visit was from a horror-tag listing.