A lot of comments here are obviously by experienced mmo players but I see more non mmo players in this game than most others I have played.
Zenimax is obviously new and inexperienced and a lot of the design choices will need to be revisited if they wish to keep P2P+sub.

Quality of Life options need to be implemented. They will be as subs drop off but lets hope they do them soon before they lose too many.

Gating respecs needs to be fixed - lower the cost and enable individual skill respecs.
5 Guilds? Just so we can have options for an AH but then only be able to sell 30 items at a time per guild....why reinvent the wheel. How about no guild size restriction and I can be in 1 guild and feel more ownership and have 1 AH. No restriction...or maybe even a world/faction AH and let market forces dictate.

Phasing that doesnt work in party. Try playing the game with friends in party - 80% of the time you will be in different phases ffs. Needs some major rework to coding.

Massive amount of qq regarding solo dungeons - easiest option is to remove the "solo" part and have the ability to bring a friend - it is an MMO after all - although it feels more like low res skyrim with occasional other ppl in it. Get stuck on a solo boss....well you are paying a subscription so you should be able to bring a friend to help. This way the hardcore can do it solo, perhaps get an achievement that goes to a title at the end cap....design choices that an experienced company would have thought of..

Public dungeons will need a rework, great concept and will work atm as the playerbase is all levelling but as the game ages and there is noone to do the dungeon with...I already see this as I play on oceanic timezone and have had to skip a few or try on numerous occasions to gather enough interest.

Higher rewards for the world bosses and rifts - on my timezone no one bothers anymore and its hard to gather enough people to attempt them. They needs to fix this with scaling to the amount of players in the fight like other mmos - make them solo possible. Seal a rift - 90% of the time there is no reward...risk but no reward..in a subscription game..please.

As a sub game it needs to cater to casual, this game sold at number 1 or 2 in most countries - thats a lot of people new to the genre and to succeed they need to keep these players. So what if they make the levelling more casual - as wow/eq2/gw2 has shown you can cater to the minority hardcore and appease the casual because its the casual that pays the bills. Mores subs=more content at cap.

I believe one major problem is that gear decay ultra-quickly, and if you die a couple of times you have litterally no armor. Making the fight extremly hard. Well, that´s true for me anyway.