01:00.0 VGA compatible controller [0300]: NVIDIA Corporation G86M [Quadro NVS 140M] [10de:0429] (rev a1)
Subsystem: Dell Device [1028:01fe]
Kernel driver in use: nouveau
It makes sense that the GRUB screen is crisp (it should be as crisp as a framebuffer session), and later when X kicks in, it uses the nouveau drivers for your gfx. I think many of us have cried several buckets full of tears because of this.
Your card is the Quadro NVS 140M, you can try to install the closed-source nvidia blob:
https://wiki.debian.org/NvidiaGraphicsDrivers
You need the headers of your kernel (so for example, 4.2-0-trunk headers), the build-essential package and of course the nVidia drivers according to the highest supported version:
either the more stable 304 (
http://www.nvidia.com/download/driverRe ... 5153/en-us ) or the newer 340 (
http://www.nvidia.com/download/driverRe ... 5164/en-us )
Later you can add nvidia-xconfig to let the system create an Xorg.conf file or do it by hand:
https://wiki.debian.org/NvidiaGraphicsD ... figuration
Do this on a non-production machine or partition, it might happen that X doesn't start at all. In this case you will have to a) fix it or b) revert to nouveau
(There is sgfxi from the smxi scripts that can do this for you, I am not a big fan of it, so first DIY and don't trust external scripts)
