[Aardwolf]

KDE 3.5 was its peak for me. KDE 4 changed everything around completely, in a worse way (like no more multiple task bars, no more easy launcher icons, introduction of hard to disable CPU hogging background processes like baloo, less configuration, degradation in contrast of scrollbars in the theme choices, etc...).

[calvinmorrison]

KDE3.5 was forked at the time and still exists as Trinity Desktop https://trinitydesktop.org/

[ACS_Solver]

If you haven't, try KDE 5 as well. I also found KDE 3.5 to be an amazing desktop and was then very disappointed by KDE 4, one of the worst software released I've used. But it was pretty much abandoned relatively quickly and KDE 5 is once again an excellent environment.