I don't want to be.. contrary.. but you kinda said something in your post which I think you take for granted a bit.

'The expansion is finally released it's a thrilling experience, there's flying mounts, and the story was actually pretty good and intense'.

I pay £24.99 for the expansion. I'm not at HW content yet but from what I hear, there is a great story, big new zones and a lot of fun to be had.

Take most games on market for say PS4 and they are £50+.

So it sounds to me like HW you do get what you pay for. If you choose to continue to subscribe afterwards, then that is up to you, but I don't think you can say it's a bad expansion or has no value because by your own admission it was a thrilling experience and I imagine it's worth £24.99 at least. The subscription fee is mostly to play with friends and level up other jobs etc in my view.