I want to second the suggestion made by
@gadnihasj and
@Tradless to make a "description-on-hover" or enlarging a single entry of a list by clicking on an icon and then displaying the first lines of the description, the cover art, artist and maybe also the amount of chapters uploaded.
Regarding SPAs, I'm also split. Most of the SPAs I've seen were slow and big. I know that that doesn't have to be the case but it usually is. If you're going through with that, please make sure that the browser history and ctrl+click and all that stuff works. Eg. the Reader, which pretty much already is a SPA, doesn't quite do what I expect when I press back (go to the last chapter) but closes the reader and goes back to the page I was on before I opened the reader, even if the url has changed quite a few times between those two events.
The next one is more of a bug report but is also quite an old issue: Please fix the links in the top navigation bar when no one is logged in. Eg. I'm logged out -> click on *Follows* -> Login screen appears, I'm entering my data and press enter -> I'm on the previous page, or worse, on /login and it says I'm already logged in. What I instead should be on is the "Follows" page of my account.
It would also be nice to have some sort of organized bug/feature reporting system for mangadex, another reported bug of mine (like others) has been lying around unanswered (not even a WONTFIX or "sry no time right now but we're aware") for nearly three months now.
As always, these are just nitpicks.