I can’t say for sure because I don’t have much of a comparison point; I’ve only been to two open-casket funerals in the past 15 years, both for young men. I had completely different reactions—yet, both times, yes, I really felt my mortality.
One of them had commited suicide with a gun to his head, so the strategically placed hat and the makeup made the whole thing weird. I didn’t want to stare, but the abnormality of his looks made it hard not to look away. That took away from any sense of peace and farewell. I would’ve much preferred not to have seen this.
The second one died in a car accident and looked like he was asleep. Seeing him was a good moment—I had a small conversation with him in my head and experienced the same thing @thorninmud mentioned—a healthy purge of grief.
Any death of someone close reminds me of my mortality. As for the caskets, I think it depends completely on my relationship with that person and how they have been set up. And when I go, put my ashes in a urn, put up a picture of me laughing, have a story-based, music intensive service, then toss my ashes from my favorite mountain on a windy day.