A friend and film maker just turned me onto After The Storm, a web doc about a category F4 Tornado that ripped through central Alabama in 2011.

Overall I think this experience does a lot of things right, especially because I found myself engaged and actually finished it.  It claims upfront to be about 12 minutes long end to end, and I think this is a great strategy to get people to commit, given how stretched thin the average attention span is these days.  Especially within the multitasking context of desktop web browsing.
This is primarily a single scroll interface (which I see becoming the norm for web doc, now that dual scrolling with trackpads are becoming standard) making navigation as natural and comfortable as mobile interfaces.
Other hi lights include the feeling of using the actual equipment in the doc, like browsing photos on a Canon DSLR, or using a flashlight to explore the inside of a house during the storm.
I hope to see more experiences like this in the future, highly recommend.