The entire experience of a radio show, combined with the culture of the 40s and 50s is absolutely fantastic (although there I times when I keep thinking how much faster cases could have been solved with DNA evidence and other modern forensics!).
Dragnet is the grandfather of ever cop show that has ever been on tv - to say it is a classic is an understatement.
I watched Dragnet on tv ages ago, and while the tv show was good fun, all the sound effects and 'atmosphere' of a radio show make the radio show superior.
I like the tribute at the end of each episode to a fallen police officer - officers that were killed in the line of duty 50+ years ago are memorialized again.
There is a fair amount of variability in sound/audio quality (which is why I only gave the performance 4 stars - the actual performance is great, but the occasional audio issues made me downgrade it), but it generally doesn't take away from the listening experience.