EP was my first questline prior to One Tamriel, and I enjoyed it, but its got several rather contained storylines that all have their good points and bad as opposed to AD which is one contained storyline from Khenarthi's Roost to Reaper's March.
Spoilers ahoy. Also, I'm a roleplayer, so my interpretion of the questlines is through that lens.
Arc 1: Bleakrock to Bal Foyen to Stonefalls
The Ebonheart Pact questline starts off with a world at war. The Three Banners war has the biggest impact on the EP questline of any of the Alliances, and Bleakrock sets the tone with a hefty dose of Skyrim nostalgia, Covenant raiders, and a burning village. Bal Foyen ups the ante as you race to warn Davon's Watch about the invasion fleet and make a truly gut-wrenching choice about which group of Bleakrock warriors you are going to help defend Bal Foyen. In Stonefalls, you again face invasion, and the consequences of driving off the invaders.
In those 3 zones, we meet the Nords, the Argonians, and the Dunmer. The Nords are tied together by clan and family, and working (badly) together with the Dunmer. The Argonians are adapting to a new way of not having to fear the Dunmer and willing to work together with everyone to make this alliance work. The Dunmer are, well, arrogant and adapting (badly) to having to work together with everyone.
These three zones did a good job of throwing me into the conflict and then hitting me right in the feels. I got to know and like the villagers on Bleakrock - boom, their village is burning. Oh, now I have to decide - do I save the docks or the fort? Either way, people are going to die. The Argonians are willing to sacrifice so much to make the Pact work, and the Dunmer constantly disrespect that.
And then there's Grandmaster Tanval Indoril, who's arrogance and certitude that he's doing the right thing gets him into big, big trouble. He's the sort of character that I love to hate. My Vestige so badly wanted to shake some sense into him and tell him to listen to his much more sensible allies, a pretty good sign that I'd gone and gotten invested in the story and the characters.
Arc 2: Deshaan, Shadowfen, Eastmarch
The second arc explores each region leading up to the recognition/reaffirmation of the Pact at the end of Eastmarch. Basically everyone takes a long hard look at it and says "Guys, this Dunmer/Argonian/Nord thing doesn't make sense. Why are we working together?" And then tries to answer that question.
Deshaan is probably IMO the weakest of the three. Its TES III Tribunal nostalgia, and basically hits the same themes from Stonefalls of Dunmer arrogance causing problems. But I suppose one should never underestimate the power of Morrowind nostalgia.
Shadowfen was cool because its the first part of truly Argonian territory we've seen, but it was memorable because of how dark it got. AD trying to kill the Argonian hatchlings? That had my heart pounding as I raced to save as many as possible, and I was angry and sad when I couldnt save them all. Shadowfen's main quest did a great job of getting me emotionally invested.
Eastmarch was pretty much pure Skyrim nostalgia. I mean, the questline does a good job of explaining how the joint effort of everybody defeats Jorunn's usurping brother and why everybody is like "Yeah we're definitely stronger together than we are as enemies so we should make this Pact thing work", but its still pretty much a laundry list of Skyrim nostalgia. I mean, we went to Skuldafn and Sovengarde.
So this arc is all about "This Pact thing...is it gonna work or are we gonna fall apart?" With the Vestige's efforts being the glue that eventually binds the whole thing together.
Arc 3/FinaleThe Rift is a tour de force as the Pact, now united, faces down the Worm Cult and their Reachmen minions. Again, the EP questline has the biggest connection to the Main Quest conflict, as the Worm Cult is broke in the Rift. There's some fun Skyrim nostalgia with the Companions, some heartbreaking reactions to that choice I made back in Bal Foyen, and everyone from Stonefalls gets back together to kill a giant and prove that, yeah, this Pact thing is going to work despite the best efforts of our enemies.
The real fun of the Rift for me was that, because it was my first questline, I was completing the Main Quest at the same time. So at the same time I was hunting Mannimarco and the Amulet of Kings, I was also kicking the butts of his Worm Cult in the Rift. Which was really freaking epic.
I really did enjoy the EP questline. Its not a single, cohesive storyline the way that AD is the story of "how the Vestige helped Queen Ayrenn save the Dominion from her impulsive life decisions". Rather, its the story of how three nations/people's with really good reasons to distrust each other and beset by war and trials came to work together to defeat their common foes. It was a immersive, heartbreaking, frustrating, fun, nostalgic, and epic experience for my first questline in ESO.