So far PVE in ESO has been relativly boring:

Bosses and mobs all have the same amount of ressistances, making for example a dks fire attacks do equally much damage against a fire atronach as it would against a frost atronach. Bosses dont have any uniqe ressistances, making them all the same, bar health and mechanics. And most of it result in people choosing the most powerfull copy-past playstyle which is best in the current state of the game. Damages done from skills are mostly the same, sorc have one line for shock, DKs have one line for fire, and other than that most class skills just do magic damage (even some when its stamina based).

So here is a few good suggestion to make PVE more uniqe and interesting.

1# Make bosses have different weaknesses and strenghts, making Valkyin skoria strong against fire damage and the Engine guardian strong against poison damage. The other would be to implement a more different ressistances in the Trials: forexample having first boss strong against physical damage but weak against magickal damage, having second boss weak against physical damage but strong against magickal damage, and third boss strong against elemental damage and poison and disease damage.

2# Make class skill do different damage depending on morph and what stat is highest. For example Having veil of blades do physical damage if stamina is highest or magicka or perhaps frost damage if magicka is highest (would make it more on equal footing with the new constaletion setup), Having burning light from aedric spear do fire damage if magicka is highest (its called burning light for a reason presumably) or disease or poison if stamina is highest. Make more use of the different elemental and physical damages, making some of NB skills do frost damage if magicka based, as icy grip of death aproaches. Or poison if stamina, with killers blade. And possible turn shock and fire damage into two variants, magick fire and shock, and weapons shock and fire (as so far they are just in magicka constelation tree).

3# Change more of the ability to make them more usefull and interesting.
Examples: Have the winged twillight choose two different morphs for either magicka play or stamina, making the magicka morph turn it into a flame atronach for ranged damage, or the stamina turn it into a dremora archer for ranged damage. Ditto for the scamp (familiar) morphs.
Go trough checks over what class abilities are barely used, and then change them to make actually usefull. (not going into a stam crystal blast or SA, as those have already been dissused) http://forums.elderscrollsonline.com/en/discussion/comment/2685104/ sorry couldnt find a good one on crystal blast.

4# Change the sets to be usefull for the specs its aimed at, so far a couple sets you would trollsor was creating them like noble duelist set which gives weap dam,stam regen and weap on 4 set pieces together, and its light armor with training traits . Other would be to actually go trough what the least used sets are and make them more usefull for theyre ligth/medium and heavy armor users. So far pvp is the place you will see most diversity in gear setups, as there is more to worry about with regens etc.

Well thats it, now just to hope that devs actually try to play the game as it is being played, and Not in whatever delusional version they think it is.