I am really happy with the milestone features. It comes so close to the memory feature I loved in the sims 2. For infants it even goes further by tying gameplay to milestones. There already is a
thread about infant milestones but I think the milestones of other ages also deserve attention.
I like that this feature is cross pack compatible. After lifestyles, sentiments and wants and fears we finally got a system that takes existing packs into account. Thank you sims team for supporting existing packs!

My sim got a milestone for graduation, for being an occult and for completing the strangerville scenario when I opened the household for the first time after installing growing together. I also like the one for the top of Mt Komorebi but my sim had to climb the mountain again after installing growing together to get this milestone.

I really like how the milestones can keep track of important social events. Finally sims have a sense of history because they can remember passed events. A refused proposal gives a separate milestone. It is a bit strange that the refused proposal has a location tag while the accepted one does not. My sim also got a milestone for being saved from death. His wife earned the good trait through self discovery while she pleaded with the grim reaper to save him.
Feel free to add your experiences.
Comments
My sim started with only ‘adopted a pet’ from cats and dogs. Then she got childhood phase, puberty, best friend, and finchwick fair milestones. It looks completely different from your selection.
I’m really glad they give them for the big achievements like winning contest or climbing mountain. High school graduation milestone seems broken for my sim though.
Havent seen any indication of one so far though...
I love that "woohoo" in Dutch is rendered "O jaa!"
This translation has been in use since the sims 2 days so I have gotten used to it by now.
There's going to be "Death of a Best Friend" in Lumpinou's upcoming (currently Patron-only) mod. A bunch of modders are collaborating to get lots of Milestones added without duplicating each other.
The project and a link to it:
Suggestion thread:
I hope the bug is fixed soon, and that the modders' work will still be usable after that.
@Elisdream This sounds like a glitch. It doesn't make sense that they would reset upon aging up. That would defeat the whole point of them.
Family trees:
Young
Pearce
Niner
Did you check the expanded view? It doesn't list everything in the simology panel.
My Families Via PlumTree App
https://answers.ea.com/t5/Bug-Reports/OPEN-GRO-Milestones-resetting-disappearing/td-p/12394945