Jedi Academy is nicknamed JK3 so you would be askign if a JK4 is in the works and so far we have had no solid evidence to that effect. To say whether JA is better then JO is entirely up to you. As the old adage goes: "One man's meat is another man's poison". Some people who left JO for JA have stayed there and never looked back. Some people has said JA was bantha poodoo and went back to JO. Then you have the minority who play both still. (like me).
My advice: research. Check out
www.lucasarts.com/products/jediacademy/) .
Read all the reviews you possibly can. If you don't want to however I'll give you a few things to think about. (please keep in mind these are MY thoughts and views)
Pros :
1) You can customize your character in terms of race,color & gender. (SP)
2) You start off with a lightsaber and you get to customize that as well. (hilt and blade color). (SP)
3) New moves to perform which can definitely help with the game's missions. (SP)
4) More force powers to use in the missions. e.g Absorb which you only got for MP in JO. (SP)
5) At a certain point in the game you get to choose between your regular single saber, dual sabers (Anakin in ep2) or a double-edged saber aka staff (Darth Maul ep1). (SP)
6) You get to ride tauntauns and fight wampas & a rancor or two. (SP)
7) New items including the grapplehook and jetpack. (MP)
8) JA+ a great mod (MP)
Cons:
1) The storyline just plain sucked. It didn't have that deep immersive feeling of JO. (SP)
2) The dismemberment code which made JO realistic when we found it out (whenever you did :)) doesn't work anymore and you have to do a lot of @#$% to get it working. (SP)
3) For MP the new moves that were good in the SP suddenly get spammed and you more or less end up on servers with kata whores or butterfly spammers. ( I mean hey they are easy to beat but it does cut down on interesting duels.)
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Anyway as i said it's all up to you.
EDIT: Almost forgot if you want to get really into a SW role try out KOTOR and KOTOR:TSL. Yes they are RPGs and I hated them too but they are really good. In fact they are the ONLY RPGs I play.