Are you a KDE user? I switched from Gnome 3 when Plasma 5 was new, the very moment it seemed close enough to finished to expect reasonable stability. It was a huge departure from KDE4, and after trying literally every other DE to find happiness away from Gnome (that's all I'm going to say about that) over the course of several years, it was such a welcome relief.

Plasma 5 was not only a life preserver for folks bailing from Gnome, it also showed they'd learned from their own mistakes with KDE4, which many users felt was just as much a trainwreck as Gnome 3.

There's a lot going on under the hood with the change to QT6 as noted, and that alone merits a version number change, IMO. I haven't tracked a whole lot of specific features, but I know there are a lot of wayland refinements and HDR support coming, and I'm doubtful that the many pointieststick blogposts have been doing nothing but writing about bugfixes and menu changes, even if I haven't read every single one of them.

The general default look and feel maybe isn't being radically changed, but this is Linux, and more importantly KDE; we're all about theming and customization anyway, right?

Most importantly they aren't throwing out the baby with the bathwater. They did it (intentionally or not) with 4, and then (in my perception) they were forced to do it with Plasma 5 because of KDE4.

After living through the transition from Gnome 2 to 3, and KDE 3.5 to 4, then feeling the relief when Plasma 5 just absolutely crushed it, I'm very happy to see them upgrading the undercarriage and making things generally better instead of building it all from the ground up again.