To be honest, in my opinion, the writing for High Isle was worse than Blackwood. Blackwood was awkward but I at least remembered parts of the story after finishing it. After finishing High Isle I had a hard time remembering what it was all about - it just seemed a whole load of nothing. Like with last few expansions, the player is a basically a lackey for the characters who are actually in charge. There are a few side quests I enjoyed but the main quest is something of a nothingburger.

You may get on with it fine as fans of the expansion do exist but for me, who bought it for the story, I found it very lacklustre.

edit -
I think perhaps, the reason why I didn't mind Blackwood so much is that it felt, despite the chaotic/weird choices that were made during the story, that there was some passion still there in its development. High Isle is bland in the extreme, there is no passion there at all. It's flat, passionless and leans way too hard into trying to be funny. A story should make you feel something - I felt nothing after this one.

Personally, I feel like it's all too wholesome/fun, it's very hard to take seriously at times, and it feels like a very PG fanfiction.

They keep pushing certain characters or little memes, they just aren't things I care for at all - like the whole Investigator Vale thing - like I just don't care, and for roleplay's sake, neither would my character; so having it constantly come up gets old very quickly.

Keep in mind, all this is just personal preference - it's not bad per say, it's just not what I enjoy or what engages me. There have been a few stories I did really enjoy, in no specific order the ones that come to mind are Morrowind, Clockwork City, Summerset, Wrothgar, even parts of the Elsweyr chapter... though I feel with Elsweyr that the less than serious trend started to get out of hand/balance a few times there. Even parts of the Skyrim chapter were decent, loved the Markarth DLC, great lore there too.

I'd like to see more mature writing, something that really pulls me in and engages me on an emotional level - make me have to go take a moment after finishing a chapter's story, just to take it in and reflect on it.

I doubt I'll really see that in ESO though, I just don't think it's the ideal medium for it, unfortunately.

That being said, I much prefer High Isle over Blackwood - Blackwood was just a convoluted mess with so many things that went absolutely no where.

The main issue with the quests in ESO over the last few chapters has been that all players are forced to be altruistic and "good". You can't side with the "bad guys" -- even a tiny little bit -- and unlike even the base game there are few to no choices you can make that affect the outcome of events in any way, or that make NPC's react differently to you based on your choices.

As an example there might be a base game quest where someone has been turned into a Vampire and you can choose to kill them to stop their predation or spare (exile) their life so that they might find a cure, and some NPC's later on in the game can react to your choice. Another good example is the quest for Phaer in Auridon, whether you kill or save the antagonist is referenced by other NPC's such as guards.

Even in Orsinium, the player spends a lot of time "helping" King Kurog only to find out he's been in league with the Vosh Rakh and Trinimac cultists the entire time, making many of your actions somewhat dubious from an ethical point of view.

Since then the player feels less like a free agent able to make their own choices and more like a passenger on a ride with only one path.

Even if you RP as an evil Daedric cultist who delights in torture, murder and sacrificing victims to Molag Bal and raising the dead, when you do the quests in Blackwood and High Isle you are forced to be the most noble, virtuous, Lawful Good player in the game, because you have few or no other choices to act in a manner more consistent with that character's alignment.

Fable and especially SW:TOR did a MUCH better job with this, by making many interactions and quests have good, neutral, or evil choices, and then the game world changing and adapting to the results of those choices over time. I wish the ESO story devs that make quests would sit down and play through SW:TOR quests for a few days, and learn that there is much value to be had in not forcing players to be saints 100% of the time.

Edit: part of that too is affected by ZOS' need to make quests affect major lore characters and events. e.g. you're forced to help the three faction leaders because if you were to able to side with the Ascendant Order instead, that would require modifying the lore for Ayrenn/Jorunn/Emeric, and it is hard to reconcile giving players meaningful choices when it comes to the lore for major characters in the Elder Scrolls.

The problem is that if you want a coherent story, then it will inevitably be linear. Elder Scrolls games put the emphasis on lore - i.e all the story is in history books - and let the player take more control of how the present plays out. Yes, there are objectives, but you can take your own path to reach them.

for me i think blackwood was the worst chapter, that story (and the related dungeons like black drake villa) actively made me hate eveli

i felt the high isle story was much better, although it still felt fairly short compared to say north elsweyr or summerset