"The Case of the Howling Dog" (1934)
In order, the four movies are "The Case of the Howling Dog" (1934), "The Case of the Curious Bride" (1935), "The Case of the Lucky Legs" (1935) and "The Case of the Velvet Claws" (1936). I won't go into the plots of each of them as they all have different flavors and have different actors/actresses playing similar supporting roles.
Warren is wonderful in everything he does so he is, of course, great as a slick lawyer type that is not above totally breaking the law to finesse justice to the best of his advantage. Warren plays Perry as an extremely charming, quick thinking, witty and urbane .... shyster type. This Perry Mason in no way resembles Raymond Burr's Perry. Warren's Perry reminds me more of what Nick Charles from the "Thin Man" would have been like if he had been a lawyer.
I would have thought the first movie "The Case of the Howling Dog" with Mary Astor would have been one of my favorites, but for some reason, it didn't gel quite right with me. It might have been me, but I found the plot a bit overcomplicated and difficult to follow. I guess they were way too clever for my feeble brain. It was a good start though, to get me in the Perry frame of mind.
The next two "The Case of the Curious Bride" and "The Case of the Lucky Legs" were both wonderful - you have Perry Mason flirting with Della Street as well as any other woman he comes in contact with. You also have Allen Jenkins as the wonderful sidekick Spudsy. Perry also joins the ranks of the charming mystery solvers that can't find a clue without a drink in his hand. There are many jokes and gags regards to his penchant for the spirits and both movies are fun mystery romps that I highly recommend.
The last "The Case of the Velvet Claws" really fell short of my expectations, unfortunately. Warren is still as wonderful as always, but Allen Jenkins didn't return as Spudsy and his absence was very much noticed. Also, the movie series totally "jumped the shark" by starting the movie with a marriage between Perry Mason and Della Street. This tempered the sexual tension between them, it also stopped him from flirting with every single woman so as not to look like a cad and it just ended up not as fun a turn as a result. It is not surprising that this was the last one in the Perry Mason series, unfortunately.
If you are a great fan of Warren William, you should probably make an effort to watch all four. If not, you will be happier just watching the first three and skipping the last. You won't be missing much - you could save the time and re-watch one of Warren's many other wonderful movies.