Lots of hard work? I can believe it...
Trying to make a shortened version of a classic film in Flash is a brave undertaking and one I've never seen actually pulled off before.
13 minutes - a long animation, but a short time in which to tell a story designed to span more in the region of 2 hours.
You did a good job of capturing the best bits and working through the story, but I still came away feeling that whilst you did a really impressive job, it ended up being slightly more tiring than it should have been.
Some suggested voices. However, having original voices would be difficult (if not impossible) and any would add to the filesize stupidly. Original voices would just annoy.
Some pointed out that you should be able to understand the flash without having seen the film, and I'd probably agree with this. It would make the think much harder for the sequel, but it would make it more enjoyable for those who have forgotten or not seen the films.
I'd also say that you should be using more quotes from the film - there were a couple of pieces of what I think are original dialogue and I didn't like that. It's nice to see the new art, but I'd suggest you change the visuals and editing but nothing else.
Some of the bits chosen could have been better. For example, what was the point in showing his CK boxers without her calling him that? Why not have the mad dance for the Johnny be Good bit, when that was the highlight of that original scene?
I did really like the split panels used for the guitar-playing bit and the guitar and note-shapes used as wipes. I also loved the excellent caricature of Doc and it was all nicely drawn with clean lines. (Although some occasional shading for moody scenes would have been nice.)
It does amaze me that someone has gone to lengths you have to have finished such a project, but it does seem to be more of an accomplishment than an accomplished piece of entertainment.
I was expecting BttF on speed, but it was only half-way there. Still, I encourage you to go further with the 2nd one. If you mull over complaints and suggestions, it should rock the boat and be a vast improvement.