I think my fellow reviewers are overstating things a bit. Roma Violenta is by no means a bad movie, but it does nothing any number of poliziotteschi films can't do better and it doesn't impress with what it does either.
Maurizio Merli plays another inspector, this time Commisarrio Betti. There's a healthy number of car chases, fistfights, gundowns and just about anything you would expect from a film of this kind, but it's all done with such a workmanlike air from Marino Girolami (Castellari's father) that I couldn't help but glance at my watch every now and then. Girolami does Roma Violenta with the get-it-over-with attitude of a professional instead of the enthusiasm of a fan. Get in, take the master shot, take the close-ups, get it over with cos there's a paycheck in the end. No imagination whatsoever. I can imagine him on set crossing things off a list: "Car chase? Check. Fistfight? Check".
Polizioto fans that need their fix will be satisfied by Roma Violenta, but if you haven't seen true genre classics like The Cynic, The Rat and The Fist, Almost Human or La Mala Ordina, then Roma Violenta can wait.