If you are looking for a game similar to another game, the following site is pretty good and can find even the most niche of games. You may want to uncheck the box to show unreleased games. The lists it creates aren't perfect, but if you actually go through the list you can usually find some interesting games.
SteamPeek uses a unique recommendation algorithm to find the most relevant, indie friendly PC games - great tool for all kind of gamers. Beside the list of similar results, it allows you to discover hidden, trending indie gems, new game releases and even coming soon titles.
steampeek.hu
Of course, the thing that makes all of these tools a worse than they should be are the Steam tags, which are often wrong. Hopefully they'll come up with an AI or something that can clean them up. With over 100,000 games, I think it's too late for humans to do it
Plus, we're the original source of the problem anyway. Let AI do it, and we may argue with it, but it should at least be consistent.