I noticed something about Tony Stark's ending.

When a main character dies in a battle, he/she normally gets killed by his/her enemy during the fight. In case of Tony Stark, his death was completely brought to him by himself and himself only as he snapped his finger while wearing that Infinity Gauntlet - knowing that doing so would mean a certain doom for him.

This is what's so different about his death compared to others. He almost literally threw away his own life so billions can live - completely by his own free will. Yes, Doctor Strange informed him that this was the only way, but he decided to do it anyway because he would rather have the option where he's the only one to die over the option where the whole world would get obliterated.