Some of us say when SunOS stopped being BSD based and went SysV into Solaris, we knew the end was coming.
I actually appreciate many things post Solaris were net beneficial. The scripted install stuff presaged a lot of what emerged as puppet/chef/ansible/helm type processes. (this is pre YAML/JSON) -The disk/drive/segment labelling scheme has been completely normalised, the BSD device/partition scheme had limits.
And of course ZFS.
Solaris 2.4 and earlier was a little rough. I no longer remember the exact details, but 2.5.1 was the first release I felt comfortable running instead of SunOS 4.x.