I'm also a big fan of Matthew Colville. That said, I really wish the guy would take a moment and breathe on occasion. He talks so fast I feel worn out after his videos end.
I'd also like to recommend High Rollers by members of the Yogscast. These guys have a great 5E actual play campaign on...
Our weekly gaming group has used flanking since we started playing over a year ago. While it really hasn't made combat unnecessarily complicated, I certainly wouldn't miss it.
I'll be DM'ing for a separate group in the upcoming months and plan on leaving it out for many of the reasons others...