I loved the dark noirish feel of s1, and the troubled characters. I loved the way they used the city too as part of the show - particularly that final scene in Blink when Mac goes to Ground Zero, that was just such a uniquely dark 'NY' moment. I believe they actually filmed that at Ground Zero, AZ says so in the ep commentary if I'm not mistaken. But I did like the lighter feel of s2 as well, and I liked how they kept up the character angst/drama with Mac, Stella and Danny's various storylines. I complain about Lindsay, but I did like the lightness she brought to the lab in s2 - I like her in that season. In season 3 I liked how they developed Mac's character showing both his softer side (Reed and Peyton) and his flaws, and the Flack/Mac conflict was great too. One thing I hated about s3 though was that almost all the cases involved rich white people or at least middle-class white people getting killed. Where did the diversity of s1 go? This is NEW YORK for Chrissakes, not Midsomer wherever! As for s4, some interesting character development, but probably my least favorite season as it's only half as long and also the people getting killed are nearly all white.
I like the angle-shots too, and the shots of the skyline. I'd love it so much if they brought back the dark feel of s1, not in every ep, just in some eps. I suppose Child's Play was a good 'dark' storyline for Danny. Oh, about Danny, I love that he's grown up since s1. I found him a bit of a whiny brat at times in s1, but now I like him much more. He's still whiny, but not as much in s1. I think that makes the show realistic- he's grown up, his personality's evolved, and that's what happens in RL.
If I had to say how I wanted NY to evolve, I'd say
1. More character development for Hawkes, Flack and Adam as well as Mac and Stella and Danny.
2. Some lovely dark, noirish eps. NY in a storm would be amazing.
3. For some cases to involve working class and/or non-white people as victims/suspects/witnesses.