Star Wars Galaxies used to be the pinnacle of skills-based gaming. Your character could select skills from 33 professions. To balance things, you could only have a certain amount of total skill points, and each skill had a different amount of points it cost. So you could be very diverse and have little skill in a lot of things, or very concentrated and be extrodinarily good at one or two things.
Your characters grew and changed as your desires change. You could be an architect one day and a rifleman the next. You don't have to create a new character to enjoy a different part of the game, which is a major improvement over class and level systems. Because of this versatility, chracters make names for themselves in their galaxy, and they are around for a long time, building a huge community. The SWG community was the best part of the original game.
However, after two years of success, the game developers decided to retool the combat system. They instituted combat levels and combat changes. They added levels and damage mitigation by level. So a lvl 1 character getting hit by a lvl 5 mob takes a lot more damage than a lvl 5 character getting hit by a lvl 5 mob. This started to turn the game into a more level-based system, as xp was majorly effected by level of characters in your group.
Six months later, the executives at LucasArts decided that the game wasn't "StarWarsy" enough, and instead of being their own individual characters, everyone really just wants to be one of several iconic figures from star wars history. SO instead of being able to be a smuggler and architect, you have to be Han Solo OR Lando Calrissian, not both. Thus was born the New Game Enchancements. The combat system changed to a twitch based FPS, and the skill system was removed. In it's place was a WoW-based system of core classes and a thinly disguised talent system (called "Expertise" instead).
Most of the playerbase left because of this. After six months of the Combat Upgrade, SOny Online Entertainment and LucasArts pushed basically a beta build of a new MMO out to every SWG subscriber. This was also weeks after the release of The Trials of Obiwan, a third expansion to SWG. The expansion included content for several classes that were removed from the game, and sparked mass protest.
Smedley, the head developer of SWG in it's current incarnation, recently issued an apology in regards to the NGE. He said that it was a mistake not to listen to the playerbase (who liked the skill based system) and that while there would not be a return to the skill system, they would be listening closely to the remaining playerbase.
It's actually a belief of mine that if Sony released the original game code as Star Wars Galaxies 2, they would recoup a few hundred thousand subscriptions.