The other big difference no one's mentioned is lighting. B&W movies today don't look like 40s films because nobody seems to know how to light them the way it was done back then anymore. Nobody knows how to create and use shadows anymore. Films of the 40s were full of shadows and bits of light strategically placed for effect. It's a lost art. Pathetic little PRC knew more about lighting than the big modern studios will ever know. Modern lighting involves flooding the whole area with as much ambient light as the camera can absorb. In the old days, lights were placed here and there as needed to create the ambience. Dead Men Don't Wear Plaid is probably the closest to the old ways that a more modern film has come, but it had to be to match the old footage it contained. It's a pity, because B&W can be such an effective story-telling tool, when done right.
Favorites:
The Maltese Falcon
Citizen Kane
Kiss of Death
Arsenic and Old Lace
The Wolf Man
Abbott and Costello Meet Frankenstein
The Big Sleep
High Sierra
His Girl Friday
Detour
All the Val Lewton horror films from RKO - yes, even poor little Leopard Man
All the radio based movies Columbia did - Fibber McGee and Molly, the Great Gildersleeve, the Whistler, Crime Doctor, I Love a Mystery, etc., etc., etc. And Universal's Inner Sanctum films with Lon Chaney, Jr.
And the other series films - Sherlock Holmes, Boston Blackie, Charlie Chan, Hopalong Cassidy, Nick Carter, Mike Shayne, etc., etc., etc. Fun stuff, all.