since 12.04 we have had unity->gnome, xorg->mir->wayland, upstart->systemd, python2->python3, iptables->nftables, addition of zfs, snap, livepatch, lxd, and dro

since 12.04 we have had unity->gnome, xorg->mir->wayland, upstart->systemd, python2->python3, iptables->nftables, addition of zfs, snap, livepatch, lxd, and dropping 32bit support. All of those were pretty major changes and definitely not just incremental. And that is just top of my head, I probably missed lot of things. On the other hand, most gnome2 era releases are pretty much a blur in my mind. What to you made those feel more significant?