Don't like the desktop environment? Change it.
Want more than four virtual desktops? Add more.
Want/don't want fancy 3D desktop effects? Turn them on/off.
You also don't have to reboot constantly to apply updates and there's literally thousands and thousands of self-updating packages you can install in seconds without having to "search the internet." And they're not just limited to "apps."
Even better: If you're developing software to run on Linux servers you can test your code locally without having to upload it anywhere and you don't have to worry about zillions of platform gotchas.
Lastly, with Linux you get access to all sorts of neat things natively that you just don't get to fool around with in other OSes like cool filesystems, virtualization tricks, networking features up the wazoo, low level access to hardware (many motherboards have GPIO pins you can fiddle with natively!), and lots of other "fun" stuff (well, I have fun playing around with the new toys that are regularly introduced :).