The ending was perfect. It wasn't "sad" but "bittersweet".

Sam was too good a guy to retire from helping people. It's like that line in Captain America Civil War:

> Steve Rogers : If I see a situation pointed south, I can't ignore it. Sometimes I wish I could.

> Tony Stark : No, you don't.

> Steve Rogers : No, I don't.

They're the ultimate boy scouts, and the show ending any other way would have been a betrayal of the character.

I will fight people on this.