If you want to try a "true Unix", meaning one that has descended fairly directly from the original AT&T source tree, whether via Berkeley or not, this is your shot. Linux is not a Unix, though it is closely related and structured in the same way. (That sort of statement can cause endless argument, so please let it go and move on :))
The link above will take you to a personal blog/review of OpenSolaris 2008.5 by one Bill Beebe that I thought pretty nice. (One of those "I wish I had written that" things.)
Jason Perlow, writing on ZDNet, has a real "rah-rah" take on it, here.
And the Practical Technology blog has a very odd take on Open Solaris, predicting more or less that it has arrived just in time to be killed off. No, really. See that here.