The weakest link in the Flash Gordon trilogy in my humble opinion.
There were things I liked about this serial and things I didn't, but over all it doesn't add up to the first two serials.
I liked the relevancy of the time, the way in which Ming now paralleled America's greatest threat, Adolf Hitler, complete with Germanic attires for he and his troops, a Hermann Goering-like Captain Torch, a reference to concentration camps, and a change of title from Emporer Ming to Dictator Ming. In accordance with Ming's transformation from Yellow Peril Emporer to Hitlerian Dictator, the way in which he was treated had changed. In the first two serials, Ming was to be sent to prison or deposed of, Flash condemning Tarnak's attempt to kill Ming in seemingly cold bood. Yet, in this serial, Flash Gordon and his companions had to eliminate Ming's threat perminantly in the same way that the serial creators felt that Hitler must be eliminated. Sure enough, it was scarcely a year later that America entered into World War II.
On the science fiction adventure side of the equation, I liked the Purple Death (brief though it was), the walking bombs, the attempt to drown Flash at the cost of Ming's own men, the cliffhanger in which Flash fights the large guard and they fall into the pit, and the camp title with Les Prelude accompaniment, but overall the serial just doesn't do it for me. The first one had a lot of cool scenery and some good fight scenes. The second one was more plot driven, presented Ming as a greater threat, and had a final battle between the hero and villain which the other two serials were lacking. However, the third doesn't seem to bring much to the table by comparison.
Roland Drew made a poor replacement for Richard Alexander as Prince Barin. Lee Powell, who played Roka, would have been better served to have played the role. As soon as I saw Drew's Barin, I knew he wouldn't be taking on the active fighting role the prince of Mongo had in the earlier serials. He was perhaps the best of the secondary characters. The action didn't stand up to either of the previous serials as well. The first serial had the battles with the ape men, orangapoid, and Prince Barin in disguise and the second serial had the struggle between Flash and Ming, but there were virtually no noteworthy conflicts in this film aside from possibly the brief struggle between Flash and Torch. I also found Ming's demise to be somewhat anticlimactic. I think that Flash comandeering Ming's ship and crashing it into his tower was exciting enough, but the lack of retaliation on Ming's part took away from any excitement. He was a trapped rat and nothing more. It would have been far more exciting if Ming had troops dispatched to shoot the Z-0 ship out of the sky and Flash overcame them en route to destorying Ming. Yet, we get Flash escaping from the guards, calling Ming's bluff, and then 15 minutes or so of talk before Flash crashes the ship and destroys Ming. I much prefered their ray gun battle from the second serial.