Most of these points apply to all non-windows OS, not just GNU/Linux based ones.
Here's my list:
Serves as a proper OS you can use, instead of the other way around
Has tools to do basic tasks such as writing a disk image to USB, CD etc without futzing around for hours and/or installing some shady package from a website with porn ads
Doesn't spy on everything you do/watch/listen to/say/who knows what else
Doesn't do who knows what else behind your back
Does its best to use your CPU, RAM, disk space, bandwidth etc. as efficiently as possible, instead of deliberately wasting them so you'll need to buy a more powerful PC
Doesn't force-shove"updates" down your throat whenever it feels like it
Gives you full control & ownership of your computer, instead of giving it to some piece of shit corporation that will profit off you forever
Doesn't automatically download & install random shit you have no interest in
...or the next "upgrade" of itself if you leave it on all night
Lets you work without shoving as many ads in your face as their market study concludes most ppl will tolerate
Pretty much all distributions have a bootloader (grub, lilo, etc) that will let you boot other OS, not a "linux-only, fuck everything else" bootloader
Unmounts its own filesystem cleanly on shutdown, so as to not hold your data hostage ie. other systems can access the volume without corrupting everything
Doesn't delete all files it decides you don't have the "DRM" to have in your possession as soon as you plug a USB stick, external hdd etc.
I could go on for days -)