A Recommended List lets you share your suggestions with other users. Each list has a category, so a list lets you recommend a specific kind of game.
The category of a list can be anything you want. It can range from something very general, such as your top 10 games overall, to very specific: your favorite one-room games set in medieval castles, say, or the hardest puzzle games you've played. You can base categories on things like subject matter, genre, setting, time to play, difficulty, intended audience... any set of criteria that you think would make a good list.
You can create as many lists as you like, so there's no need to fit all of your favorites into a single list.
If you're looking for recommendations from other users, you can look for a Recommended List using IFDB's Search feature. If you can't find any lists with the sorts of games you're looking for, you can create a Poll, which is the reverse of a list: it lets you ask other IFDB members to recommend games in whatever category you describe.