I used CDE (and thus Motif) for many years. It may look outdated now, but it was years ahead of its time. While it may not be as usable as, say, GNOME 2 or KDE 3 were, it's actually still managed to be better to use than GNOME 3 or KDE 4+ have been.
I have seen CDE a few times (e.g. on Solaris), and found it very unusable, so much so that installing KDE or GNOME was much easier than trying to just use CDE.
While KDE 4.0 was very rough, and 4.1 only addressed the roughest edges, from 4.4 KDE has had almost complete feature-parity with KDE 3. At least they aren't applying non-optional Mac-like interfaces (where the menus are 100s of pixels away from the Window they apply to like GNOME 3). It's quite frustrating using GNOME 3 apps (about the only one I use is simple-scan, as I'm not aware of a KDE scanning app that scans to PDF).
Plasma 5 and KF5 are now also very good and quite polished.