having played and GM'ed SWRPGs since the D6 WEG days, there a few things that work well for each system that cater to different playstyles:
 
D6 - (WEG) - Strength:  Very Cinematic and story driven gameplay.   Weakness:  Heavy reliance upon the GM's ability to craft not only the proper mood, but arbitration of Combat Rules.  the free-form combat and general gameplay rules with nothing to back the GM up besides a "Because I am the GM & I said so!"  makes for what should be a funny, dramatic, & overall exciting experience into a stressful outing for fledgling GMs or for GMs unfamiliar with the universe.
 
D20 - (WOTC) - Strength:  Robust combat & class structure.  Weakness:  strict Character Creation guidelines and very slow combat gameplay kept players & GMs from pushing their imaginations.  Once combat started, gameplay slowed to a crawl. even basic combat encounters took the entire session to resolve…  especially with the Force mechanics.
 
D20 SAGA - (WOTC) - Strength:  Balanced rules structure and combat mechanics.  Weakness:  Underdeveloped & contradictory rules sets as well as inconsistent publications.
 
Color me biased, but Saga Edition was the best of both worlds between cinematic and tactical RPG gameplay.  Certainly not perfect, it did ride the line and for the most part had the Star Wars feel in its combat structure and character creation (thank you D20 Modern  ). 
 
things to consider when developing a new SWRPG system:
The one thing none of the other Game systems were able to accomplish effectively was the ability to go from "on-foot" conflict to vehicular conflict in a seamless & cinematic manner.  no matter what system you used,  it was always a difficult transition to give chase in an encounter whether it was D6, D20, or Saga.  D6 was the smoothest, but Saga had the most potential.  also, please include chase mechanics too 
Vehicles are characters too!  Flying in an X-wing or a YT-1300 is great,  but it was always troublesome rules-wise to make it "Your" Starship.  and forget about trying to make super weapons or prototypes as a GM!  if you are going to make a new SWRPG system, FOR THE LOVE OF ALL THAT IS HOLY PLEASE INCLUDE IN THE CORE RULES FOR GMs & PLAYERS TO EASILY CREATE, MODIFY & USE VEHICLES EFFECTIVELY!  fantasy games already have ironed out the other mechanics for a SWRPG,  it's the vehicle rules that all others have stumbled over.
Being able to fail upwards toward a goal is integral to the Star Wars experience.  unfortunately it is also the piece that most RPGs gloss over or simply ignore in their mechanics.  what I mean is this-  Stormtroopers & Battle Droids still need to be feared by players from time to time and need to be more than just scenery after level 2 or 3.  likewise Big, Bad, Evil Guys need to be able to be a palpable threat to the bitter end.  to tell an epic story,  you need EPIC VILLAINS!  D6 did fine with that, but only due to ridiculous dice rolling (50d6 for Vader's force Choke!).  A "Hard Mode" mechanic would appease not only knit-pickers, but Epic storytellers as well    
 
 
and there's my 2 credits of input  
 
 
May the Force be with you Fantasy Flight,  we'll be watching you