I know I'm using an old entry level laptop (specs in the end), but I'm having problems with instability with Elementary OS that I never had with Gnome Shell and lighter DEs like MATE with Compiz, whenever I change brightness (it always happens, the exception being change brightness again a few seconds after doing it the last time), and sometimes even starting to type, opening the menu or changing volume causes a freeze on the system (I can move the mouse but can't do anything), most of the time it freezes for like 1-2 seconds but sometimes it can take up to 10 seconds for the system to recover. I checked system monitor and whenever I change brightness, I have a spike on processor usage up to 100% in just one thread. I thought it might be due to swapping but it happens even when there is below 1GB of RAM usage and no swapping.
Specs: Intel Core i3-3217U (2C4T, 1.8GHz), 32GB SSD where the system is installed + HDD for data, 4GB 1600MHz DDR3 RAM, Intel HD 4000 IvyBridge graphics. Temperatures are fine and the processor usage is usually pretty low, except when viewing videos on Youtube or having constant swapping.