deep characterizations, character-centric plots, occasional story arcs / recurring plotlines, and -- for a time, anyway -- the ever-important romantic tension between the leads.
Which all used to be absolute anathema to the very concept of L&O....
That was my favorite bit: L&O was absolutely character-proof - there *was* no characterization. That's why I liked it so much - the story was literally everything. If Mr. Spock was a TV show, he would be L&O.
And I still haven't forgiven CI for getting rid of the doink-doink and text captions.