I am not an OS guru but it seemed to me that Solaris is by far the most powerfull kernel available for the x86 platform. Good kernel don't mean good and user friendly OSs, but Solaris has, IIRC, virtualisation and filesystem features that linux and windows could only dream of. It's Unix firepower for your home.
With Oracle swalowing Sun I'm afraid we'll live the same situation as with DEC back in the days: a decade from now, we will look back at Solaris and Java technologies and say 'man, they really invented everything'.
On a side comment I wonder how such companies manage to remain largely unprofitable with such good technologies in their portfolio.