One of the big problems with modern franchise based RPGs is a lack of stability. This wasn't an issue in earlier eras; West End Games held the license for Star Wars for some 11 years, while FASA held the license for the popular rival franchise Star Trek for some 7 years.
While the Star Trek RPG license has been doomed over the years to languish without proper support (or in some cases no support, going from FASA from 1982 to 1989, then Last Unicorn from approx. 1998 to 2002, and then Decipher from around 2002 to 2005, with a few "non-cannon" versions from Amarillo), the gaming universe has been more generous to Star Wars, with the D6 version from approximately 1989 to 1998, and with Wizards taking over (in fits and starts) from 2000 to today (with a few periods of no releases and minimal support).
While the D20 was well regarded (particularly by me, since I like he D20 system), the newest incarnation (the "Saga Edition") attempts to streamline the rules and present them in a new, cohesive whole. The philosophy behind releases very strongly follows the "sourcebook" model, with new supplements covering a variety of subjects, rather than just one topic (with some notable exceptions, though even Starships of the Galaxy, and Threats of the Galaxy tend to have a bit more information than just what the title suggests). The result is a series of "era" books that do nicely in fleshing out the time period in Star Wars fictional history, but also provide enough of a mechanics draw to make them worthwhile if you do not play in that specific period.
In reading the books, especially with the launch of D&D 4e a year or so later, it becomes immediately obvious that Saga was a "testbed" for some of the concepts of D&D 4e. For example, when attacking, you no longer neccessarily roll to hit the AC (armor class) of the target, but rather the reflex defense of the character. This does create some "wonky" rules, such as armor adding a bonus to Reflex defense, but unless you are a pedant, in my opinion, this isn't such a big deal (at least for me).
Overal I am around 90% happy with the Saga rules. Force powers, though limited (you can use them only once per an encounter, unless you spend a Force Point to recover it, or roll a 20 on a force use check) feel like the setting, and despite the fact that Saga is very similar to D&D 4e, it doesn't hit you over the head with the Grail of "COMBAT BALANCE!!!!" that D&D 4e attempts to enforce. While both games have a sort of "talent tree" mechanic, Sagas is far, far more open ended, and isn't a forced combat mechanic (believe it or not, there are talents that are useful in GASP! role playing opportunities), and there is a lot more freedom in what you can choose just in the core rules!
Furthermore, the streamlining of the rules are sensible and add to the game; nor do the rules overtly punish players for their choices. For example, D&D 4e punishes players for mounted combat, and the rules for that are, at best, cursory (with the recommendation "don't do it!"). On the other side, since vehicles have always been a big part of the Star Wars universe, vehicle rules are supported in the core, and expanded in other books (such as Starships of the Galaxy).
In the end, though, are the rules perfect? Not in my book. While I'm mostly satisfied, and enjoy playing the rules, there are a few areas that make it less "chrome-plated" and more of a highly buffed, burnished steel.
One gripe I have is the skill system. The Saga skill system is very similar to D&D 4e's, and one I'm not thrilled about. In essense, characters get a skill bonus of half their level to all skills. Thus a 20th level character will usually have around a +10 bonus to ALL skills (assuming a build that doesn't have any ability penalties). While I can see the appeal to this (they're HEROES!), since I am a huge fan of skill based systems, this doesn't give me the satisfaction of enough "crunch" and optimization I enjoy. While the new skill mechanic is still an open ended roll (in that there is no "skill" ceiling, which is good in my opinion), in this aspect I think the previous D20 editions were superior.
Another area I dislike is the idea of armor providing a bonus to reflex saves, and not the Damage Reduction in the previous edition. The Rules As Written in Saga state that when wearing armor, you add the armor bonus to your Reflex save. Not so bad, if a little weird. However, when not wearing armor, you add half your level (just like skills), meaning armor quickly becomes irrelevant as you gain levels (unless you have special feats). Sure, you might wear armor to get the equipment bonuses or enhancements to abilities (if appliciable), but other than that Obi-wan wore clone armor just as a fashion statement I suppose...or Darth Vader so he could look evil. This doesn't sit well with me.
But then what do I like, and what do I see as improvements? One obvious improvement is the level of support. When the first D20 edition of Star Wars came out, support virtually died after a few years. With the Revised edition, it came back, but then died off to nothing again. With this edition support has been steady, with a release every 2 months or so. Even better, the releases are written by a core development team, so there is a lot of consistency across the releases. There has yet to be a release I have been completely dissatisfied with from a quality standpoint.
Another mechanic I really enjoy is the Condition track. Unlike the Vitality/Hit Point mechanic used in previous editions (where you occasionally got a spectacular result, but most of the time was still an HP hack), if you take enough damage from a specific hit that goes above your Damage Threshold, you take cumulative penalties, from -1 to -10, simulating the accumulation of serious wounds. In addition, there are certain abilities and/or weapons that might affect the Condition Track as well, and certain abilities (like the "Second Wind") to get you going again. While not exactly an original mechanic, its a good one and well executed.
Furthermore, this mechanic is repeated on ships and vehicles as well, giving the game a unified mechanic and prevents page flipping.
In the end, I'm really enjoying the Star Wars campaign we are playing in lieu of D&D (which came to a staggering halt after over 10 years of continuous play thanks in part to 4e, and a little bit of fantasy burn-out), and will happily play it as the "main" campaign for years. While the specter of yet another edition change hangs over the franchise (it will happen, you know it to be true), at least we might know how D&D 5e will play.
Saga is everything D&D 4e should have been.