I just installed the nvidia drivers on fedora 23 (kernels 4.2.3 and 4.3.5), and it worked fine for 1 or 2 restarts, but during my last few reboots, cinnamon has crashed and started in fallback mode (fedora 23 with cinnamon) and upon further investigation I saw that it was loading the nouveau driver.
Not sure why nouveau driver would cause cinnamon to go into fallback mode (or if that's happening for an altogether different reason)
So I tried forcing X to use the nvidia driver.
Section "Device" Identifier "GTX 550-Ti" Driver "nvidia" VendorName "NVIDIA Corporation" BusID "PCI:1:0:0" EndSection
What happens when I boot with these X options, is a "unable to handle kernel paging request" bug, (kernel seems to crash but doesn't say kernel panic; I'd share the message but don't know how) and I'm all out of ideas. The drivers seem like they're working outside of X though, and the kernel paging bug doesn't occur until X is started.
To confirm that my system is working on nouveau, uninstalling nouveau fixes cinnamon's crashing error. I guess what's happening is cinnamon trying to load Nvidia drivers, crashes, and goes to fallback mode on nouveau drivers where it doesn't crash. Xorg.Log didn't seem to provide any useful insights (it didn't throw any errors, just tried to load Nvidia driver and then all of a sudden switches to loading nouvau instead; it doesn't seem to successfully load any of the nvidia driver)