Here is my opinion what i think will be wrong with the game and what i feel will be great.
+++ Graphics and enviroment
+++ crafting and tradeskills
++ quests you will come randomly by not just static questgivers (the world will feel more alive)
+++ an interactive world just like in previous ES game. Honestly if ZOS will pull this out correctly it will be something not yet seen in mmos. By this i mean manipulating/ picking some items.
However now lets talk about the part where i feel like ESO will fail.
- - - PVP: Honestly no real world pvp. PVP only in cyrodill and only some big fights. Honestly imo this will be laggy zergfest. Yeah you can become emperor but thats probably the only reason why even pvp. No real point to pvp. No rated arenas or some skill measurement.
- Skills: Diablo 3 type of skillset. You can only choose 6 skills simultaneously which honestly isnt enough for mmo. Yeah there will be many skills to choose from but sooner or later you will want to play the best spec and be bored really soon.
- raids and dungeons: Well this is the part that will determine the success of ESO. We dont know much about this yet but we atleast had one video from dungeon. One big + will be that the graphics are nice so there is potential to create epicly looking raids/ dungs . However With only 6 skills available at time I feel like the dungs will simply be too easy and bosses and fight uncreative and unfunny.
+- Megaserver: I dont think this is a good idea but maybe I am wrong. This is a big questiomark for me.
So to sum it up i think the game will be amazing for about 2 months but once people realize there isnt much to do endgame the population will slowly decline. Overall i think the biggest problem will be diablo 3 style combat with only 6 skills where the skillcap will be very low.
So please ZOS remove only 6 skills max a time do epic (hard) end game raids/dung and the game will be amazing ! Otherwise it will fail very fast.