Argh, I could talk about Mr. Arkadin for DAYS. It is an incredibly interesting film, and even in its imperfect form, it is pretty captivating, and evident that Orson had another masterpiece in the chamber. For whatever reason, I find the clearly flawed more interesting than the perfect diamonds, and Arkadin is the definition of this tendency.
The Criterion set is my favorite of all Criterions. The essay book that accompanies it does an excellent job of explaining the complicated logistics of the situation, and it also comes with a novelization of Mr. Arkadin, along with several of the radio plays based off of it and The Third Man (Mr. Arkadin is a sorta prequel).
In short, not only did Welles not edit it, but he never even really finished shooting. There are some insane visuals in that movie. I <3 it. I have watched all of the cuts of it so many times, and read the book, and I am STILL guessing at how Welles was approaching it.