This, fundamentally, is ESO's problem. It can't decide whether it wants to be an MMO or an Elder Scrolls game. Many a time I've waltzed carefree through a dungeon almost completely devoid of enemies, because most of them are designed to be explored by only one person, and someone has run through it before me and killed everyone in sight. At the same time, the enemies respawn so quickly I often found myself fighting them on the way back after completing the objective, which is absolutely ludicrous.
Occasionally, the game will use phasing to give you a sense of influence within the world. At the end of one particularly long quest-line, which involved saving a giant tree (this is as thrilling as it sounds), the enemies surrounding the tree all disappeared. "Great!" I thought, "I've finally made a difference." But I then had to backtrack through an earlier battlefield where, again, players were fighting the enemies I just fought to get to the tree in the first place.
Now, the frequently respawning enemies aren't necessarily the problem. For better or worse it's standard MMO design. But the game is so insistent about your own significance that whenever it does basic MMO stuff like this, which is all the time, it reveals the true nature of your insignificance within the world, and the effect is incredibly jarring.
Not only do the awkward merging of MMO structure and Solo content fail to complement each other, they actually exacerbate many of The Elder Scrolls' worst problems. The series' most questionable elements have for years been the quality of writing and voice acting when it comes to specific quests. If you thought they were poor in Skyrim, wait until you hear The Elder Scrolls Online. It's generic fantasy nonsense in the extreme. Imagine somebody running up to you in a field and shouting the following in your face:
"We're dealing with a literal undead uprising! Our patrols sweep the wilds while our primary wizard, Gabriel Benele, searches for a magical relic that will help."
The majority of quests you'll encounter are variations upon this theme. There are a couple of exceptions. The most exciting quest I encountered came within the first couple of hours. A dog randomly approached me, and led me to a body that kicked off a pretty entertaining questline of spies, assassins, intrigue and betrayal. Yet even when the story reaches above the formula of "villagers in peril from [monsters], kill monsters/use quest item to receive [loot item]", on a systemic level the game remains deeply unsatisfying.
Almost every non-combat action you do in game is performed by pressing E. Press E to perform elaborate sacred ritual. Press E to alleviate complex and virulent curse. Press E to win game. Sometimes a quest will require you to press E on three things instead of one, just in case you don't feel like you're getting enough of that hot E-pressing action. If your character needs a hammer to do the action, a hammer will appear. If it's an axe, an axe will appear. It completely trivialises the importance of the very actions the narrative emphasises, creating an unpleasant disconnect between yourself and the game world.
While ESO makes Skyrim's biggest problems worse, it also lacks the most fundamental component that makes The Elder Scrolls games so alluring; freedom of exploration. At first you'll marvel at the sheer size and variety within the world; the towering volcanoes of Morrowind, the crystalline beauty of Skyrim, the verdant, picturesque greenery of Daggerfall. You'll yearn to explore this vast landscape, plunder its dungeons, embark upon adventures all of your own. But the strict levelling path severely limits where you can go and what you can do.
Venture into another area, even to a distant location in the same area, and the higher level creatures will pummel you into dust. Meanwhile, plundering dungeons on a whim, or indeed doing anything that isn't a quest, hardly ever offers any rewards. The game has few surprises, and no emergence or spontaneity to it whatsoever. It is a theme-park MMO of the most robotic kind, incredible to look at, but with no real life of its own.