Ive never had a problem with this either, but try using stun or stasis (if you have it), then throw grenades at it from a distance (if it is stunned than its defence drops).
I liked the fact that you could become alot more powerful in KOTOR 2. My Sith Lord was so cool, frying everything in sight with force storm.
I also prefered the way the games saves are stored, it was alot easier to find the character I wanted to play(I have 2 brothers, and they both play KOTOR alot, with about 4 profiles each, and I have about 10 profiles)
Another reason they arent different in the films is because the Jedi would have kept to tradition, and like someone else mentioned, they are just simple robes. How could they possibly change?
To level up to a prestige class, you must be at least level 15, than you must talk to Kreia, and she gives you the choice. It basicly gives you the choice to become powerful in two areas (e.g. good with the force and with weapons)