Number 3 is a children's film. Sure, there's violence and swearing, but the antics in it are something I expect from a Disney movie. The return of Serge, The popcorn gun, that pathetic ferris wheel scene... ugh.
To top it off we only had what- three of the six main characters back? And one of them died in the first scene, and had no purpose other than to try and make the film darker and personal, like the last two whose personal death and gunshot attack get the film rolling. Never once did I buy his Chief's death as anything more than a plot device.
The real difference is that the entire film is just plain old unrealistic. I don't buy it for a second. The beauty of the first two films is that back during the 80s, I could have easily seen some hilarious slick as **** cop pulling all that crap in Beverly Hills. I mean, the most far fetched moment in either of the first two is when Billy blows up the truck with the rocket launcher by accident. The third film has an endless barrage of these cheesy, unrealistic moments.