I think Welles's greatest work is his essay/documentary film "F for Fake" examining hoaxes and what is real. The Criterion Collection contains an excellent documentary concerning Welles's later years. It's probably remarkably similar to how a lot of us make films today...guerrilla style, skeleton crews, no budgets. Pure filmmaking.
Touch of Evil is a noir masterpiece, on par with Kubrick's "The Killing." Pay particular attention to Welles's use of audio...this was a hallmark of all his work, stemming from his early success as master of the radio drama. The chase at the end involving the extensive use of radio transmitters is one you'll not soon forget. I was first in line to see the restoration based on Welles's notes.
It's a shame money never allowed for a fully realized, giant Welles Shakespearean production. Chimes at Midnight (his own take on the character Falstaff pulling from Henry IV and Henry V) is a brilliant example of understanding the bard from a contemporary point of view. Macbeth is a hard watch...Welles had the cast record the dialog three times (in a Scottish brogue, in regular English, and with an British accent), laid the tracks on top of each other, played them back live in the studio and had the cast lip sync. Interesting experiment, but muddy soundtrack. Othello is nothing short of brilliant, and I think it won the Cannes Film Festival when it was finally
complete. Some great shots and a terrific example of how to make low budget look extremely rich. Read the making of Othello for a great how-to.
The Trial is a surrealist masterpiece on par with Naked Lunch. Again, one of the biggest sins of cinematic history is that there doesn't appear to be a good print of this film. There are work arounds available online that involve recording the soundtrack to a separate track, slowing it down a certain percentage, and making a new DVD.
Ambersons is gorgeous storytelling...and would have now been considered a masterpiece alongside Kane if the studios hadn't been so scared of Welles by that point and chopped it to half its size with a phony happy ending.
The Lady from Shanghai is another good adventure tale and features a great shootout in a hall of mirrors.
Mr. Arkadin shows a lot of promise, but is a real hard watch, again due to bad prints. There may be a Criterion version of this, but I haven't seen it
Kane deserves ever accolade it has ever received but Welles's filmmaking career is rich and full of discovery. His style never stopped evolving. It's popular to say that he could only go downhill from Kane, but I don't buy it. He's an inspiration to me, and I think his best work was never finished. My fave, and the closest example of his
filmmaking aesthetic fully realized before his untimely death, is F for Fake. Seek it out.