Descent into Avernus has been noted as D&D meets Mad Max. This adventure is a more mature one, but most of its content by default is around a PG:13 rating which can obviously be raised or lowered by the DM. It is meant to be an intense and challenging adventure where player characters are often in over their heads.
Every Dungeon Master has a mile long scroll of things they would love to share, myself included. It’s important to note, there are very few objectively wrong ways to play D&D. The following is purely my opinion and how I run my games. Use them, abuse them or ignore them.