The spin-offs are bad. The suspects are interrogated until they confess, and nobody cares if they have no lawyer or they use dubios evidence.
For the cops, prosecutors, and defense attorneys, the show doesn't give the proper sense of immense caseload. Each episode feels like they're focused 100% on a single thing, when in reality they're probably juggling dozens, and stretched thin.
The cop side of things in L&O is fairly unrealistic, but imo in more minor ways for pacing than anything egregious.
The prosecutors of course don't get called on 4th/5th amendment violations as they normally would, and my memory is the defendant testifies way too frequently (for homicide cases, in that time priod). And it doesn't do a realistic depiction of the rate at which people get completely screwed over by corruption. And it doesn't do a great job pointing out how often prosecutors will take cases prioritized for their own political careers.
I am not a lawyer, and the lawyers I watched L&O with were civil litigators not criminal litigators, so some of my perspective is probably off (though I suspect in ways that are more favorable to the show). Also it was like 25 years ago? Lol