I think one of the most exciting things in d&d is leveling up and getting new abilities, and it is already slow going in in-person games, so in PbP it is really painful lol. I think the prospect of a nemesis or rival is really interesting, I've never had that before in a d&d game. But overall I think a diverse game, one with a good amount of combat and teamwork but also with a good amount of roleplay and room for character expression is, is the best. Mysteries and puzzles are tricky because they can be really satisfying to figure out but really frustrating if we can't. So usually I think it's best to avoid them lmao.