I really enjoyed siberian fox. I think that it showed some real imagination and was fun to play. In my view, Firelord and Fox are the two best missions around.
There are a hundred authentic military missions with real tactics and so on, and i like to play those too, but those missions are a refreshing break. I tried to make a mission around a Special forces team who respond to 'terrorist' attack on an arms factory, but the transport gets destroyed and the player is the only one who escapes. He gets captured taken to a nuclear weapon facility which has been hijacked (i created a massive facility around the maulden airstrip), and he has an oppourtunity to escape. Thus ensues a full on Metal gear Solid style mission sneaking around and so.
The mission is highly cinematic - something that is missing from most missions. The plot gets revealed through numerous cutscenes and things like bosses battles, russians, tuxedo clad kgb officers and so on.
I got about 60% then gave up. It is a shame that more missions that push the ofp boundries do not exist, as mission design will start to become more stale. Sci-fi is too much, but most people don't care if a certain add-on gun has the screws and accurately placed like the real gun, or if the tactics used 100% reflect the tactics once by the portugese army in 1987. It doesn't matter about total accuracy. Try to have a bit of fun, originality and cinematics in the missions.