D+ releases making of documentaries for the Marvel movies, but other than that, they're few and far between. I was pleased when the John Wick Blu-Rays had them, and the features were as long as the movies. The main thing with streaming is they cut all those great DVD/Blu-Ray features, and as someone that's always enjoyed them, that's a real disappointment.

Oh, and the Lord of the Rings appendices on the collector's editions are THOROUGH. You could be watching those for days if you're not careful.