Eerie, grimly realistic and tense to the point of vocal outbursts, Rainbow Six's tactical approach to planning a mission before executing it lends to a really interesting trial and error concept, helped along by the feeling of sheer joy when a mission goes perfectly.

That said, I would find whoever came up with the stealth missions and have them arrested. PS1 port was my first experience with it and the first level in the embassy is burned into my mind.