Having played ESO quite a bit more since my impressions post awhile back, I have had time to really delve into the game a bit more and come up with more that I like and a couple things that I am having reservations about. The reservations are not enough to make me cancel my pre-order but they are things that worry me. One of them is much more worrisome than the other because of the lack of information concerning it. The other one is a done deal and is something I will have to live with in the long run.
The PvE Endgame
ESO has a robust PvP endgame. The AvA is well-done thus far. Its fun, runs well and they avoided a lot of pitfalls that Guild Wars 2 ran into with their WvW. The PvE endgame, however, is much more ambiguous and ill-defined. There is very little information out there about what it will consist of and how it will work.
Its no secret that I prefer PvP but I was once a pretty hard-core raider. I did the entire 40-man raid gamut in WoW. Molten Core, Black Wing Lair, AQ40, Naxxramas. I did them all in Vanilla WoW. I don’t do that anymore and have no plans to do it in the future but an engaging PvE endgame is still important to me. The problem is, we have no idea what that will consist of in ESO. No idea at all.
Zenimax Online has said very little about their “Adventure Zones”. We have no idea if they are raids or something different. They are for larger groups but we know nothing else besides that. Zenimax has been extremely tight lipped about them and that worries me.
This article on MMORPG.com has a bit of information:
Adventure Zones are areas that will open up beyond level 50 to give high level PVE’ers something to play with. Massive open PVE-oriented areas.
Another article states this:
The developers have spoken very fondly of these “adventure zones” that kind of act as an open world dungeon, where the creatures become more difficult, the loot becomes that much more epic, and the stories go much deeper than any of us are even going to be able to fathom.
Three endgame options were mentioned in the video once players top out at level 50: Cyrodiil PVP, heroic raids, and what Zenimax called “adventure zones” where players could overcome tougher challenges by themselves, in a group or a bigger, raid-sized groups. At one point players were seen taking on a giant bone construct, possibly a world boss or other big challenge players would presumably need to group up to overcome.
That last article mentions raids and adventure zones as separate entities, which is interesting. If adventure zones are open world content, with open world bosses, this could make for some old-school style PvE and that might be a good thing.
Still, until we see it in game, its all developer speak. No one, outside of the developers, have been able to try out the adventure zones or any possible raids. There have been no videos and no first hand accounts to be found. As good as adventure zones sound, this worries me.
The MegaServer Concept
If you are not familiar with ESO, you may not know that there is only one server for North American PC players. Everyone is housed on one server ( which is, of course, made up of many, many actual servers). There are many advantages to this, no having to plan out what server you and friends are rolling on. No having to worry about servers with too low a population or too high. No having to worry about server merges or paying to move to another server.
Lots of upsides but I can think of plenty of downsides as well. The first of these is the total lack of special server rulesets. No more PvP servers, no Role-playing servers. None of that can exist so there is no way to cater to a particular play-style. Role-players will be dumped into the general population. PvP players will never see a server in which they can invade the other faction’s PvE zones to gank. That kind of sucks.
The next problem with the Megaserver model is the phasing problem. Each zone has many different “instances” running at one time to alleviate overcrowding of the zone. This creates problems where you may be in one instance, while your friend is in another. You can travel to him but its a pain and is currently buggy in beta right now. It also reduces immersion in my view.
Right now those are my two biggest worries around ESO. I think I will eventually get used to the Megaserver but the PvE endgame is a big concern. Zenimax needs to release more real information about raids and adventure zones soon. Hopefully, they will surprise us with a big reveal before release because the lack of information is disconcerting.
Corpse Run 
I share your concerns over mega servers, while I like the idea on paper, as an RPer, I’m going to miss the atmosphere of people in character. I personally would like to continue my Elder Scrolls tradition of playing a Dunmer devotee of Azura.
Apparently, they are going to have a questionnaire when you first log into the game. This is going to cover stuff like playstyle, whether you roleplay etc.. People with similar interests will then have a higher chance to play with like-minded players in each instance of each zone. How well this will work, I do not know.
I don’t roleplay, though I respect those who do. I have played on many roleplaying servers, however, and I find them to be a more mature populace on average. The main reason I have rolled on RP servers in the past, is simply because I see less stupid names. Nothing irritates me more than a player named Ipwndu or an elf named Legolass. It irritates the hell out of me.