Pre-NGE, specifically Pre-CU:
There were 33 professions. You could mix and match these professions to your heart's content. Making for a truly unique character. My main at the beginning was a Master Teras Kasi, Master Swordsman with a smattering of Fencer and Pikeman skills (I could solo a Krayt Dragon!!!). My alt was a Master Bounty Hunter, Master Carbineer with a smattering of Smuggler and Pistoleer skills. There were far more combinations, including non-combat options, and you could truly tailor your character to your play style.
Combat: Your toon had what was called HAM bars. (H)ealth, which was a red bar, (A)ction, which was a yellow bar, (M)ind, which was a blue bar. Your skill sets depleted one or more of these as each skill typically drew from one or two of them to fuel the skill. This was something you had to micro-manage strategically in combat. WHICH WAS A GOOD THING. It made combat strategic not a spamfest of skills or constant rotation (i.e. 1,2,3,4..1,2,3,4...rinse and repeat). The reason you had to micro-manage was if you depleted any one bar too fast then your opponent(s) could utilise an attack that specifically attacked that bar which would in turn knock you out temporarily. Once knocked out, they could focus on your health bar and kill you. There were also snare attacks and knockdown attacks and stun attacks.
There were no levels, it was all skill based.
Jedi: Jedi was a hidden profession. You had to master an unknown number and unknown combination of professions to "unlock" an extra character slot that became your Jedi. Jedi WAS A LIVING NIGHTMARE to level. You had to do it in secret. If you were seen wielding a lightsaber or using Jedi skills by other players your name eventually ended up on the Bounty Hunter terminals and a player Bounty Hunter could hunt you. This was canon as SWG was immediately after A New Hope and Jedi were still hunted and scarce. Eventually, though, you became strong enough to not be too afraid of being hunted and it was not so lonely. As to the actual levelling.... holy hell... Each profession's skills were found in skill boxes. It took a certain amount of combat xp or class specific xp earned to unlock a particular skill box. Starting at 1000xp to cap at 300,000xp for some Master boxes, 600,000xp for other Master boxes. Jedi skill boxes STARTED at 1,000,000 JEDI xp, not combat xp nor any other xp. Needless to say it took A LOT of time and effort to level a Jedi. Each skill box was an accomplishment of epic proportions and mastering a discipline was cause for a 72 hour celebration filled with wine women and partying. Dying as a Jedi was the worst!!! You lost PRECIOUS xp when you died.
I mastered 27 different professions before unlocking my Jedi. I eventually ended up with a Master Lightsaber, Master Defender, with Enhance and Healing skills and I chose not to spend any xp in Powers. It goes without saying that there was a large amount of pride and accomplishment for such a feat as mastering a Jedi.
Pre-NGE but after the CU:
They now assigned levels to your character somehow based on the number of skill boxes you had mastered. This was pointless as someone could master a slew of the lowest boxes and still show the highest level. Someone could also have mastered all the crafting or entertainer professions (NON COMBAT) and still show the highest level.
Combat was not all that different but they did get rid of snares, knockdowns and stuns. Which made being a melee class difficult versus ranged classes.
Jedi: almost anyone could be a jedi, though it still took work. now all you had to do was travel to this hidden village, perform tasks, unlock a special set of "force sensitive" skills that eventually led to Jedi skills. The xp was still a nightmare and you still had to do most of it in secret, but the village took the mystery away. All you had to do to become a Jedi was a series of quests.
Remember Remember the 15th of November....THEN there was the NGE.
33 UNIQUE and mixable professions were brought down to 9 "iconic" cookie cutter professions. No one was different. EVERYONE was the same.
Jedi was a starter profession. One of the 9 "iconic" professions. And had become utterly useless because they were a melee class, the only melee class fighting in a game designed for blasters and lasers.
Combat became point and click. Target your mob, hold down the mouse button, 1,2,3,4...1,2,3,4 until dead. Move on to next mob and rinse and repeat. Again, Jedi became useless. All a ranged class had to do was target, hold down the mouse button and kite a Jedi all day long. A Jedi could not attack anything or anyone unless they were within melee range. They eventually improved a Jedi's combat effectiveness, though.
It was dumbed down beyond belief.