I have yet to convince anybody to play Jovian Chronicles, but the system (and that setting in particular) has always seemed very attractive to me.
At the most basic mechanics level, the system is based around "tests" against a threshold. When rolling dice in a test, you take whatever number of dice (generally your skill or attribute rating), all d6s. You take the highest value of all the dice. If more than one 6 comes up, add one to the total. So 2, 3, 2 = 3; 1, 5, 4 = 5; 2, 6, 3 = 6; 2, 6, 6 = 7; 3, 6, 6, 6 = 8; and so on. If *all* dice come up as 1, you've fumbled. What this basically means is that thresholds of greater than 6 are pretty difficult to beat, and the higher your rating the less chance you'll fumble.
In addition to this, situational modifiers can add directly to the die roll. So you might have a +2, in which case you take the roll as above and add 2.
Untrained tests, you roll two dice and take the *lower* of the two rolls. So 2, 3 = 2; and 1, 6 is a fumble.
Complexity in skills is actually pretty interesting, I think. It lets you model two somewhat independent ways of "knowing" a skill. A character with a high skill rating in a low complexity doesn't have much breadth of knowledge, but is very experienced. (Many dice means few fumbles, higher averages in general.) A character with a low skill rating and a high complexity has a large amount of knowledge, but little practical experience. (Less dice means more fumbles.) The mechanical way it factors in is that a skill test can have both a threshold and a complexity. The difference between the character's skill compelxity and the test's complexity acts as a modifier. So a player with 4/2 (a level of 4 with complexity 2) who attempts a 6/1 task needs to beat a threshold of 6 with 4 dice, and has a +1. A player with 2/4 needs to beat a threshold of 6 with 2 dice, but has a +3. Likewise, if the complexity of the skill were higher, the lower complexity character would have a penalty to the test result, while the higher might still have a bonus. It's sort of your basic accuracy vs. precision trade-off.
Each complexity level costs a bit more than the same skill level, but they can add together nicely. 4/1 costs 16 points, 3/3 costs 18 points, and 2/3 and 3/2 each cost 13 points.
Finally, a little bit more about how this mechanic extends:
DP9 stole the ideas of "taking 10" and "taking 20" for the latest edition, using the names "taking average" and "taking high". Taking average allows you to take 2 + skill level when not being hurried or threatened. Taking high allows you to take 4 + skill level by spending 20 times as long as long as a fumble won't cause bad things to happen. Really, the +2 and +4 and 20 times as long isn't quite right statistically, but they're nice round numbers.
Combat is generally done using opposed tests--your attack skill against the opponent's defense skill. The degree of success (how much you beat the defense roll by) is multiplied by the weapon's damage multiplier to find out how much damage you do--and that's then compared to the target's wound thresholds--if it's less than a flesh wound, it's not counted. Between flesh wound and deep wound, it turns into a flesh wound (-1 penalty for each, cannot sprint or run, but can jog.) Between deep wound and instant death, it turns into a deep wound (-2 penalty for each, one deep wound means you can only walk slowly, more than one you can only crawl). Past instant death, well, it's pretty obvious. In addition, every wound you take can knock you out--you have to succeed in a Health (attribute) test (including the above modifiers) against threshold 1.
So getting hit at all in Silhouette is bad news--combat is much more deadly, I think.
The one piece I find a bit overly complicated is the stat system. There are ten primary attributes and five secondary attributes which are derived from the primary attributes using formulas. (Like Strength is the average of Build and Fitness, Health is the average of Fitness, Psyche, and Willpower, Stamina is 5 x (Build + Health) + 25.) This seems needlessly complex, but only really has to be calculated once, I suppose.
Vehicle combat is very well done, which should be no surprise--DP9 also has some very nice tactical war games based on the same rules. The rules are fairly straightforward extensions of the same principles as described above.
Hope this info has been somewhat useful.
I occasionally wish I could convince friends to give a Silhouette based game a shot, if only because it would be fun to use something besides d20 rolls once in a while.
