The sluggishness, in my experience, depends on several factors:
* Which toolkit is used (if any). Tk-based apps seem to be very quick, since Tk is pretty spartan and basic. GTK-based apps are okay. QT apps aren't quite as OK. Pure-X apps are zippy, but they're ugly as heck.
* Which WM/DE you're using. GNOME3 and its relatives (Cinnamon, Unity?) are sluggish as heck. KDE and GNOME2/MATE are much more tolerable, with or without desktop effects. (Open|Black|Flux)box are zippy, as are cwm, Emerillon, WindowManager, and virtually all of the tiling WMs. Enlightenment is zippy sometimes, but I don't think I've ever managed to get it to run without crashing back to a login screen within 5 minutes of use.
One curious thing I've noticed is that system resources have absolutely no bearing on UI zippiness. Whether I'm on a PowerBook with 512MB of RAM or a gaming rig with some Intel Core i9-867-5309-Quakemaster-Ludicrous-Gibs-Edition-whatever and terabytes of RAM with some NVidia GeFarce GTXXX 5-million-CUDA-core 8GB SLI monstrosity of a video card with hardware-accelerated 3D grass rendering, GNOME will always act like it's running on a God-damn ENIAC.
* Which toolkit is used (if any). Tk-based apps seem to be very quick, since Tk is pretty spartan and basic. GTK-based apps are okay. QT apps aren't quite as OK. Pure-X apps are zippy, but they're ugly as heck.
* Which WM/DE you're using. GNOME3 and its relatives (Cinnamon, Unity?) are sluggish as heck. KDE and GNOME2/MATE are much more tolerable, with or without desktop effects. (Open|Black|Flux)box are zippy, as are cwm, Emerillon, WindowManager, and virtually all of the tiling WMs. Enlightenment is zippy sometimes, but I don't think I've ever managed to get it to run without crashing back to a login screen within 5 minutes of use.
One curious thing I've noticed is that system resources have absolutely no bearing on UI zippiness. Whether I'm on a PowerBook with 512MB of RAM or a gaming rig with some Intel Core i9-867-5309-Quakemaster-Ludicrous-Gibs-Edition-whatever and terabytes of RAM with some NVidia GeFarce GTXXX 5-million-CUDA-core 8GB SLI monstrosity of a video card with hardware-accelerated 3D grass rendering, GNOME will always act like it's running on a God-damn ENIAC.