Variety is the spice of life, as they say, so I'd like to see variety.
There are obviously going to be Stormtroopers, Dark Jedi and Probe Droids. As for the other Imperial types, who knows?
Personally I'd like to see a Bounty Hunter or two. An Assassin Droid might be good, especially if it was tough. Pirate raiders would allow a lot of flexibility in races, and different weapon/armour combos.
Should there be Rancors and Wampas? I don't know. We had them in MotS, but they could probably be implemented much better now.
What I wouldn't mind seeing is some kind of betrayal...like a Jedi who helps you through one level, but when you near the end of the game/mission, they turn on you without warning.
I guess they could come up with original stuff, too, like they did in MotS with those statues.
The Mailocs could return (those flying things), if they move a bit faster (a speed similar to the things in Heretic 2 would be okay).
I thought the water creatures in JK were the weakest of all, especially the Water Cycs (not sure of the spelling). They never moved, and two shots from a distance with the bow-caster, and they were dead, so they were pointless, IMO.
Any underwater threats should be fast and mean and lethal, IMO. Maybe like those big fish on Naboo. And talking about underwater - if those levels could be something similar to the ones in Rune, it would be great!
There could also be another flying enemy - maybe a bunch of hard-cases on repulsor-sleds taking shots at you. Or maybe they could use jet packs a la Boba Fett.
Heh...just imagine having to fight a bunch of resurrected Mandalorians...that could be fun.