1. The game brings to you the full continent of Tamriel, which of coarse to anyone that is very exciting. But for the more lore buff's and veteran players(since arena to morrowind) it is a displease. This is because with all the area they need to make and cover, it won't be as detailed as a traditional Elder Scrolls game.
2. The mechanics of the game. Many gamers that started out playing before Oblivion had already had so much of the game mechanics taken out, for example major and medium skills, speechcraft, myticism, the ability to cummon creatures from the oblivion realm, slow fall, levatation, and many others. If the Elder Scrolls online goes the traditional way, or even slightly off, then the mechanics and combat system will be completely different and not traditional Elder Scrolls.
3. In most if not all MMO's the exploration value is almost taken out of the game, having certain areas only accessible by higher levels or more skilled players. This takes out the true exploration value that the Elder Scrolls is most famous for, and I would hate to lose that.
4.(KotOR gamers can relate) I am one of the Biggest fans of KotOR 1 and 2, and was very excited for SWtOR. But unfortunatly, after a month of playing, I still could not find the same feeling as I had with KotOR, not even in the slightest, itjust felt like another generic MMO.
But, that being said there are still a few ups to this.
1.Zenimax and Bethesda(Iknow it's not bethesda making it but it has helped drastically) have always been some of the most advanced and innovative and genre game changers out there. Take a look at when Morrowind was released. There was litteraly no other game like it. It set the standard for games,. Then came Oblivion where they out did themselves again, and raised the bar, only to exceed that bar with Skyrim. For thsee reasons, I hold hope.
2. The Elder Scrolls Online takes place 1000 years before Skyrim(800 before Morrowind and Oblivion) which means completley new lore with the already presented lore. Dwemer and all the great houses of Morrowind, High rock still split into different kingdoms, old alliances, and new ones we may not have known of.
All in all, it is up to Zenimax whether or not this is a make or break game. These are my ideas, please discuss yours.