By 1944, although the credits still said "Bob Kane" for contractual reasons, Dick Sprang was firmly entrenched as THE Batman artist on "Detective Comics". In volume four, covering "Detective Comics" #s 87-102, published from mid-1944 through mid-1945, Sprang brought a dynamic and distinctive cartoony style to the Dynamic Duo. The numerous Batman writers seemingly realized just how unique Sprang's style was, and started writing to those strengths. The result was a series of fun, light, and imaginative tales that were a far cry from the early and decidedly grim stories.
Even though Batman had a solid rogues gallery by this point, there are still only two Joker and two Penguin stories. The Penguin stories are both interesting, as the show that, once upon a time, the creators knew how to make the character appear a legitimate threat. The second story, "The Temporary Murders!", is the better story, as the Penguin kidnaps several people, freezes them, and refuses to thaw them unless he receives a hefty ransom. Needless to say, Batman and Robin soon find themselves under threat of a deep freeze.
While the Penguin was a threat, the Joker had noticeably softened since his first appearance in "Batman" #1. In his two stories, the Joker seems far more interested in pulling big stunts, including the theft of a building in "The House that was Held for Ransom." While the Joker does his best to kill Batman and Robin, he isn't the bloodthirsty monster he was in his early stories (and was a prince compared to the character as he is written now.)
One villain, the Cavalier, makes another appearance in these pages. A couple of things make this character interesting. First, there seems to have been some intent to make this character Batman's opposite number, as we learn that the Cavalier is a sort of bored, rich playboy who turned to crime to enhance his personal collection of mementoes. However, this character seems to have pretty much vanished at some point. I can think of one Batman story from the 1980s wherein the Cavalier among other villains, tackled Batman, and another from the 1990s with a different character under the same name. Otherwise, he seems to have simply fizzled out.
Aside from these villains, most of the stories found in this volume feature Batman tackling gangsters, smugglers, and other mundane thugs. However, they still make for entertaining stories, as Batman brings justice to some pretty rotten characters, and helps out plenty of sympathetic folk. Strangely, Batman and Robin didn't beat up on too many Axis agents in this volume. That's true of Batman generally; while there are one or two memorable stories where he fought Nazi sabateurs, Batman stayed clear of current events.
The big flaw of this volume is intrinsic to golden age comics: it is extremely formulaic. Batman and Robin discover evil, they attack the vile henchmen, the henchmen somehow get the upper hand, capture our heroes, and place them in some sort of clever-but-escapable trap. Thus, it's very easy to read these stories and develop a sense of deja vu. That's not per se bad, but it is something that one should remember, and take in stride. Don't let repetition ruin this vintage treasure.