Personally, what I'd like, for old and new enemies alike, is more uniqueness:
- some enemies (animals, atronachs?) should not use the most advanced attack patterns that the AI now provides;
- some enemies (spiders, scorpions) could strafe more liberally than others;
- some enemies (rats and bats? but not only) could sometimes spawn and attack in packs;
- maybe some enemies (spriggans?) could only attack when cornered;
- some enemies (thieves-like) could prefer ambush or outflank than straight combat, given the choice;
- some enemies (skeletons, zombies?) may not feel pain so not turn around when attacked from behind;
- some enemies (harpies, nymphs ?) could have temporary blinding attacks;
- I'd like atronachs to get the area-around-caster elemental damage they were planned to have in classic Daggerfall; Talking of that, have all the (dis)advantages listed in the
bestiary been implemented?
- maybe ghosts and wraiths could not be stopped with doors. I'm not sure about walls. Not being stopped by any wall may not be a good idea, as they could attack thru the ceiling, for example;
- some enemies could only appear in some regions, or local features (mountains, nearby waters,...) so you'd have to travel around to get different dungeoneering flavors; Maybe there's some region without the spiders that keep paralyzing you...
- ... etc
I'm certainly missing some obvious stuff (should probably go back to mythology and d&d books for inspiration) but you get the idea, that would make encounters more tactical. For this, make enemies behavior modular, then flag each enemy type to use some of the modules; that could then be used to add new enemies with other behavior combinations.