I think I've nailed down the main difference between old "Law & Order" and the reboot.
The old one felt organic, a bit gritty and grimy around the edges. Like, yeah, the main sets were constructed, but they were constructed in gritty, grimy old buildings in downtown New York City. That if you walked through the ready room to get to Lt. Van Buren's office, you'd smell sweat and stress and stale coffee from decades earlier. And the outdoor scenes weren't largely populated by extras, but the actors were filming around real people on the city streets or in the subways going about their anonymous business. When McCoy was wearing his heavy coat, you felt the deep cold and when you saw Lennie Briscoe in his short sleeves, you knew the pavement he was walking was sizzling hot.
You don't get that with the new show. It's too crisp, too clean. It's too precise. There are no rough edges. It's too... packaged. The stories are familiar enough - the format is tried and true. The actors range from serviceable to quite good, and the chemistry will strengthen with time. They just need to smudge it up a bit.
Let L&O:SVU and L&O:Organized Crime show off the shiny things and the mood lighting and the sometimes odd camera angles. Law & Order needs to be as every day and scuffed up as a pair of well-worn duty oxfords.