We need to be clear about what Board & Card Games isn't: it's not a site for soliciting people's opinions on game quality, nor is it a database of board games.
As soon as I read the "defined-list" argument I thought of all the closed questions we have of the form "What's a good game for n players?" When I first started participating on this site, I was tempted to ask such questions; I was excited to find a group of experienced gamers and I wanted to find out what their favorite 5-player games were. Now I agree that they're not good questions, so I'll try to use them as a context for my answer.
Bad question 1: What's a good game for 5 players? (Optional additionsFrequently seen with: Community wiki! One question per answer, please!) This is extremely subjective.
Bad question 2: What games can you play with 5 players? This is just boring. It's objective, but it's a database query, not a good Q&A question.
For both of these you can do a Board Game Geek (BGG) search and sort by ranking. In the event that you're looking for a field that's not recorded in BGG's database then you could head to their forums (BGG: Gateway Board Games). BGG is a site for discussion and opinions.
Good question 1: What is a 5"5-playerplayer" game? Okay, so this one isn't a goodparticular question isn't great because it's so obvious, but the type of question is good: terminology. The original "What is a Gateway Game" question is an example of this type. It's a good question.
Good question 2: Five can be a difficult number of players to find a good game for. You can't have even teams, and turn-based games can get feel slow unless turns are short. What characteristics can a turn-based game have so that it doesn't feel totoo slow with 5 people?
A good answer for this last question should cite some games (after all, answer from experience!), but specific games should not be the answer. For example, games like Dixit or Apples to Apples have have everyone involved on every turn, 7 Wonders uses simultaneous drafting so that people are taking their turns at the same time, and Citadels has very short turns, many of which have some interaction and suspense for everyone. But the examples are just that, they provide back-up for the main points of the answer.