One of my favorite parts of KotOR was where you first board the Star Forge and there's quite a few Jedi vs Sith battles going on -- this really added that "Epic" feel to the game. I would definitely like to see more of these epic-scale lightsaber fights in the sequel.
The parts of the game that send "waves and waves" of enemies at you was a lot of fun too. There a great sense of accomplishment when the battle was over. IMHO, send 100 guys at me in waves, make them easy to kill so I can mow them down like a Jedi really does ... that, my friend, is fun; a really long, continuious fight!
Additionally, I would like to see some flips & jumps, etc. into basic lightsaber combat.