Here are few reasons, why Fading Suns is one of my favorite science fiction roleplaying games.
Rules Are Good
If I have understood right, some guys behind Fading Suns have been working with White Wolf before (Mage, maybe Changeling too, but most definitely mage...) And you can see something from oWoD in rules.
Basically, you add attribute with skill to get target number, similarly like in oWoD. Difference is, that range in Fading Suns is 1-10 instead of oWoD's 1-5. In oWoD, you roll numbers equal to your attribute called dice pool (roll dice and all results that meet target number are considered a success) when in Fading Suns you try to roll below the target number with D20 to success.
But there's a trick. Even though you try to roll below, higher number is still better. There is Victory Chart, where higher number gives more "successes" than lower. For example:
If your character's target number is 13, and you roll 4, you do success but get less Victory Points than rolling for example a 10. Really cool system, but basically you have to refer every roll to Victory Chart (included in character sheet).
One problem there is though, damage is rolled as dice pool (Victory Points + weapon damage = dice rolled against target number of 13). This might be a bit confusing, because system is different for different kinds of things. Also, dice pool is rolled using D20, what is a lot of uncontrollably rumbling dice on the table.
Even though I like the system, it works smooth, I think that it could be a bit smoother. Still, I haven't have problems using it, so it's good enough.
World Is Really Interesting
I like the background story of the game. Basically, it's year 4996 (notice, that the game was published in 1996) humanity has reached the stars and had it's glory in advance, but then it descended back into middle ages and now world is mix-up with middle ages, priesthood, laser weapons and space technology. Cool isn't it.
There are so many possibilities for adventures. You can run basically anything between middle age fantasy to space opera.
Also, there are aliens, but not too many of them. Few basic alien races, one mysterious and one hostile (not sure if there are more in source books, but this is enough for me as you can design mutants, human-animal hybrids and animal aliens still being loyal to setting).
Good Experiences Of Play
When I got this game, my gaming group was not very interested in it (fantasy-heads). Had few test runs I guess, but cannot remember any details. I only have had two Fading Suns campaigns, but both of them were over 100 game sessions (last over 150!) So, even though I have had basically only two campaigns, they were really long and rich in incidents (I have to look back those with my player, and write about them later). I don't lie much, but those two campaigns were easily worth of double the campaigns. This game for me and my player is the one, that when you pop you cannot stop. Once Fading Suns starts, you don't dare to stop.
I know, there are newer editions than my ancient first edition, but frankly, I am not interested in them. I like my first edition, it works fine. I don't want to read my game once again with a bit different twist, because this is what I am used to (same with oWoD to nWoD, or for OSR players 4th edition... I guess) play. I could want some source books though, just for additional ideas (this far I have used my Agent Valerian encyclopedia, Farscape and other science fiction for inspiration). Oh, and an extra copy of Fading Suns 1st edition core rules book would be nice, my print looks like it's been in a barbarian war of space.