Lack of a good and unified system administration tool like SAM (HPUX) or SMIT (AIX).
Expensive Storage System (DiskSuite with fancier LVM and filesystems)
Lack of migration support. Sun did not provide a lot of tools to ease migration. Many applications wouldn't run in the binary compatibility mode. The source compatibility mode was probably compatible with some OS, but it certainly wasn't SunOS. Lots of public domain and third party stuff that was needed wasn't immediately available for Solaris. NIS+, buggy, resource hungry and unstable replaced NIS in incompatible ways.
Back-compatibility needs to be improved ('tooltalk' not 100% compatible with older version).
