Ooh, I LOVE this series!  One of the few series I picked up on Blu-Ray, I just HAD to have the trilogy on BR, lots of interesting stuff to be shared, and I'm always finding out something new - like how in the second film, Old Biff was actually filmed as fading away in pain coming back to 2015 after giving Young Biff the sport almanac - the idea being that Lorraine finally had enough and shot him dead.  Pretty dark stuff for such a light film!