I do not know whether I would go so far as "one of the best RPG's of all time".
I loved the game at the time and I believe it helped propel RPG's to the specularity we have now.
Going back and thinking about the game, it created a very good groundwork for Interface Management, suspense and narrative...
But does it stack up to some of the later breakthroughs in RPG's like the Elder Scrolls series? Or even D&D series (though lately, they suck)?
One of the bests, sure why not I say :) Many games took that groundwork, from original Deus Ex to recent Prey.
Not saying that Elder Scrolls are not great, both are in the Mount Olympus of RPG's.
As I say, for it's time and innovation it certainly deserves to stand in the hall of fame for gaming breakthroughs, but the game itself is not as endearing as more recent titles like Neverwinter nights that was released slightly after.
If you asked me about Neverwinter, I can tell you all about the lore, history and story of the game...
I really struggle to remember much about the game direction from System Shock, even though I played it to death.
It all depends on your personal preferences, some people like fantasy more, for me if there is a good story and atmosphere mixed with excellent gameplay, theme is not that important. I too know a lot about Neverwinter Nights, I played every game in the series including expansions :)