These days, Windows constantly gets in your way with ads, forced updates, crappy apps that install themselves, useless features like Cortana, forcing you to make a Microsoft account, etc. Linux or the BSDs, however, usually give you a bullshit-free and distraction-free experience. Plus, no spyware, completely free, endlessly customizable, and low resource usage (if you use a lightweight setup, but even "bloated" distros like Ubuntu and Mint are often light compared to Windows).
And what surprised me? I guess the only thing that surprised me is how easy the experience is, especially for things like gaming, which Linux has historically had a bad reputation for. Also, how nice it can be to use the terminal, not that you have to, especially as a novice user.