and installing a new desktop because the latest Nvidia drivers for my card breaks the functionality of Unity desktop (Nvidia is such crap).
There I fixed your spelling mistake (Linux to 'Nvidia').
Nvidia drivers are in no way a fault of Linux. Nvidia is notorious for not making very good Linux drivers, or caring all that much about Linux. There is in fact a video of Linux Torvold giving Nvidia the finger because they suck so bad at working with Linux and improving their drivers for their hardware.
Mate is a good desktop interface anyway, so its not all bad that you had to switch to that. Once the next version of Nvidia drivers comes out give that a try and see if it fixes the problem with Unity, it might.
Saying that, glad you got steam working. I personally haven't had that much problems running it on Linux. Typically a quick 'apt-get install steam' does the trick and I can get into the GUI application. Of course running some of the games is usually the challenging part since not all work all that well yet.