First thing I noticed is being warned that the installer's certificate was expired — but I was allowed to continue. So not a biggie, but the certificate used in the 2.1.6 installer still isn't expired if I install today*.
Second thing was that the installer failed without any further info. Having been warned about the certificate previously, and looking in Console that was being flooded with trustd/kextd messages, I initially assumed it was a certificate issue, but then trying to re-install 2.1.6 failed as well, even after running the uninstall-make-run.sh script in the 2.2.2 DMG. After two tries and monitoring Console while the installer ran, I noticed an error about the OS not being able to unload a zfs kext, as there were 3 "instances" or something to that effect.
Light bulb, I concluded the installer had failed to unload the kext initially, and yet continued to try to install on top of it. I re-ran the uninstall script, rebooted, and the installer now succeeded.
Just an FYI
Thanks for the new version.* Sidenote: I'm convinced that this has to do with older root certificates having expired in KeyChain, and I've previously had a bunch of gripes getting Yosemite to run various software due to certificate issues, so if anyone has any info on projects/howtos that help deal with certificates on older macOSes, I'd love to hear about it
EDIT: It is also completely broken out-of-the-box once installed, as reported here: viewtopic.php?f=26&t=3457