Hi,
First, I'll tell you that I love this game - beautiful scenery, excellent voice over, thoughtful quests, etc. etc. Well, as long as I play this game solo with occasional instant cooperation with unknown players who just happened to be around to kill a hard boss. I.e. if it were a single-player game I would easily call it the best game ever.
But, a very important aspect of MMO is cooperation with friends. And this is where the game is terribly bad to the point of being not worth playing together. Yes, there are dungeons designed with cooperation in mind, but the 99.9% of the game to me is questing (did I say I love the quests in this game? I do!) and exploring together.
Questing is totally broken because the virtual reality is not shared.
Well, at first glance it looks just a bit awkward. We are in the same team, but we both have to talk to the quest giver and if somebody lags a bit behind, watch how friend talks to empty air because in my reality the quest giver moved to a different position.
Then it comes to realization that the quest goal is not shared. "Hey, adventurer, go disarm 5 traps!". OK, I see a trap, but my friend runs ahead and steals it from me! Hmm. should I better play alone?
But the final blow is the locked doors. Say, I already did that quest because my friend was busy with real life. Now he comes and we try it again. OK, I patiently watch him talking to air and doing actions I do not understand because I do not see what he sees and hear what he hears. But then he disappears behind the door that was open to me when I was doing this quest, but now it is closed! The party is broken beyond repair.
To a less extent this is applicable to exploration. Couldn't resource nodes be big enough so both of us could get that ore? Resource stealing is party breaker. Yes, this is not hot things are in real life and it would hurt immersion just a bit, but I value team playing higher than immersion. This is MMO, not a single-player game, the trade-offs are inevitably different.
Yes, there are interesting problems to solve if you want to implement shared reality. But there are precedents too. GW2 does it good enough. The story is terrible, the NPC are pathetic, but the experience is shared. So, sorry, but now when I meet my friend in game, we quit TESO and switch to GW2.