Everyone here is grabbing popcorn, so I think I'll just start.
- Built in package manager.
- Full control and customization.
- No ads.
- Open source.
- Effective workflow. Most dev environments were planned for Linux initially.
- Lightweight (arch linux, debian, lubuntu, and many more), so capable of running smoothly on older hardware.
- Bash is way faster than powershell, and don't even joke about batch language, please. It's not even a language.
- Nice, rock solid and stable file system (ext4).
- Teaches beginners to be very careful when they run commands such as
rm -rf / or chmod 600 /
/
- I use it, so it must be good!! :P
- Get to brag about it!
- Unlike Windows, reboot doesn't solve 95% of the issues. So you actually have to know your system and the problem to solve it.
- Vast and diverse community.
Here's a funny and very true illustration..

There you go.