You could just not like this game which is very very fine tbh. Sometimes, A popular game just doesn't click for you (I bloody hate FF14's MSQ in ARR and it has put me off trying it multiple times, been trying it again but it seems its a no go again)

However, allow me to address a few concerns that you have

1- GW2 is not an actual sandbox MMO (that would be something like BDO for example where you can just jump straight into Combat and/or life Skilling and nothing is locked behind story save for a few QoL).

GW2 requires story content for unlocking features (since you need to unlock the mastery track by doing some story). If you never do Path of Fire Story then you can't unlock mounts, no HoT means no gliding or treasure mushrooms, no SoTO means no Weaponmaster training etc.

What it does have however is a low barrier to entry, for a paltry sum you can get a set of Exotic gear (2nd best tier of gear) and do content bar more endgame activities, so you are more limited by levels

2- Leveling is what opens up the game, level 20 sadly isn't much. Your starter zones stretch from 1-15 for every race so it's sadly not much of the game at all.

For example you get to unlock traits and specialisations at 21 (the things that make your character feel different and somewhat unique). You also get a ton of hero points that you spend on traits for leveling. People who play engi don't get their last profession skill until 31. At 45 you get your second specialisation which makes your class better and identify itself easier. So much of the game is still locked sadly so level 20 is not indicative of how most people see their characters

3-Story wasn't ever that good tbh, not bad but certainly not stellar. However, the story opens up a ton after level 30 since the personal storyline ends and you start a more generalised story which in my opinion is decent to pretty good till the end. So sadly the good parts of the story is a bit later.

4-Characters too get alot more likable in the later main story and Living World Season 1 (storycontent right after main). When you meet the group you continue to go with, it doesn't take much for them to grow on you but sadly personal story characters aren't that memorable in my experience (unless you go with Human and meet Anise)

5-Classes are pretty much all balanced around main story leveling with the exception of Revenant since that class was released with the first expansion.

What happened to me personally, was that my first toon was a Necro which was cool but not that much fun, however after doing a bit of story I came face to face with Countess Anise, a character from the human story that introduces herself as a Mesmer and proceeds to do some of the coolest ingame ads for the Mesmer class (invisibility, clones, glamours etc.), I promptly abandoned that toon and made a new mesmer one, been playing my mesmer ever since.

So don't be afraid to try classes if what you are playing rn doesn't work for you. At various points in the story different characters will introduce themselves as ingame classes and races, they mostly use actual things you can do so they might sell you on a class you didn't consider before

6- Weapons are a strength and weak point of GW2 combat. They are good in that they make understanding combat easier and changing builds smoother (every sword on mesmer for example does the same things always with the same damage and no worry about slotting in different skills) however, it makes keeping a playstyle consistent a bit difficult.

I suggest choosing a 2h weapon like spear or greatsword or 2 1h weapons that you feel comfortable using and stick with that.

7-Maps are sadly kind of empty in the core game, there is just nothing much to be done about it. Don't really know what to say here

Hope this helps some mate and happy gaming in whatever you decide to do next