A beautiful setting with overly-complex game mechanics, Skyrealms of Jorune works best as an incredible sourcebook for science-fantasy role-playing. The world of Jorune is unlike any other you've encountered in role-playing with rich cultural and historical details akin to those of MAR Barker's Tekumel.
Jorune has its own pseudo-magic system based on Isho, the energy that emanates from the planet itself. Character races are wide and varied, from one of three different human races to a trio of biologically-uplifted races, the woffen (uplifted wolves), crugar (uplifted cougars), and bronth (uplifted bears). The non-player character races are really the most fascinating of all. The cleash, a nasty insectoid race, the giant pseudo-reptilian corastin, the tall, exo-skeleton-armored ramian, and the mystical eyeless shantha are just a few of the intelligent races inhabiting Jorune. The non-intelligent races are even more bizarre and, one can argue, more dangerous than the intelligent races (who can sometimes be reasoned with - maybe - for a price).
Like Tekumel, Jorune's humans are descendants of colonists who have been cut off from their home planet (Earth, in this case). While ancient technologies (read hi-tech weapons, etc) do exist, they are very rare and very valuable. There are also some high-tech items native to Jorune, most notably those constructed by the shantha.
Skyrealms can be played on its own, but I find it best to borrow elements from it and shoehorn them into other systems, mostly OSR systems, such as Labyrinth Lord, Lamentations of the Flame Princess, or good old AD&D. Translations take a bit of effort on the DM's part, but everything but the usage of Isho (equivalent to "mana" in some magic systems) can be ported over effectively. If nothing else, Skyrealms of Jorune shows how a sourcebook ought to be done. The artwork throughout is beautiful, the anecdotal fictional sources are entertaining and teach the reader what it means to live on Jorune, and the depth and breadth of cultural information is truly amazing. Jorune has a bit of a cult following out there, small, but dedicated. Seek them out, and I promise that your campaigns, whether based in the Skyrealms or not, will be enriched.