- Binary log files, which are also prone to corruption and crashes
- Unnecessarily complicated and unfamiliar init script structure. I feel like I went from one that was arguably too verbose to one which is too vague.
- The need for unnecessary things like dbus to be run at startup
- Complication of some simple configuration tasks (in my experience on Arch at least, network configuration was a bitch)
- udev has apparently been hijacked and may cause issues for those who don't want systemd
All in all, it feels like change for the sake of change to me, I see no advantages which I desire, and several minor to moderate disadvantages, but learning and using it is pushed on me for no reason. Personally, I've moved to running FreeBSD, it's simple and stable, though I've been considering Debian/kFreeBSD, I'd be sad to see it go. But it's the farthest of the issues with systemd IMO.
As far as your boot time improvement goes, that's great, but modernly, my systems are either always online or suspended to RAM or disk, rarely rebooted.