Not an expert, but as a learning experience I wrote a board game recommender years ago based on data from boardgamegeek. There were a lot of little things that

Not an expert, but as a learning experience I wrote a board game recommender years ago based on data from boardgamegeek. There were a lot of little things that added up: 1. Everyone interprets the 1.0 - 10.0 rating scale differently. 2. Most users just rate the same, universally known games. 3. For the other users, the games they've played are usually really different. It's a sparse matrix. Every attempt at game-to-game analysis flopped. User-to-user analysis seemed to work better. I managed to find a few dozen similar users. Found some hidden gems by going through their pages manually. Fewer than I would have hoped though.