So two things that are important to note here, the first is that the 'fun' part of the web was learning new things and static HTML, even dressed up with HTML5 goodies, will be fun if you don't know these technologies but no more or less fun than doing the same thing on a Raspberry Pi or something similar. Its the 'learning' that is fun, and the web was more 'fun' when you were learning it because it was all new, and once you learned enough about it to see it for what it was, the parts that are less seemly start to dominate your vision and it feels less fun. Which brings us to the second part.
The second part, and I don't have a good solution for this, is that folks will use this, and they will put good content on them and they will get page views and searches and what not. Then the 'link authority' of neocities will start to rise because, well it has a bunch of good content.
Once it crosses a threshold (which is sadly pretty low) then a crap ton of SEO types will start creating pages on it to boost the organic rating of various web sites. And then Google will penalize neocities, and the good stuff will become unfindable (on Google at least) because Google won't index it, or they will pump down host rank to the point where it shows up on the results on page 3.
Just prior to that people will build sites on it that do drive by malware injection using javascript. The preferred cloaking vector for that these days seems to be a script reference that points out to something that looks like jquery but really isn't.
Then the owner is going to get a lot of threatening letters from lawyers who were told by people who got hijacked to "get the bastards who did this!" and the bad guys will be well cloaked but the neocities ownership will be just standing there, an easy target (for hassling at least, register your DMCA agent right now if you haven't already to avoid the copyright trolls).
And at the end of the day the real reason the web isn't fun anymore will become apparent. There is too much money to be made by manipulating it, and so its full of bad actors who are chortling away while stealing billions of dollars from hapless 'lusers.'