Miami focuses on the main players, the CSIs more than regular CSI, and so the cases tend to be simpler, as they have less time to spend on them. I still like it, but it has a soap-opera feeling to it that bugs me, and Horatio is a tit.
Initially, NY feels bland, washed out. That's partly the cinematography, and partly the dry character of New York and New Yorkers. The show also spends less time on it's characters, and more on the cases, making the cases more challenging, but the show feel like it has less charisma. After watching a few episodes, however, you begin to realise that the lack of character is simply because the CSIs in NY take an exceptionally professional attitude toward their work. While regular CSI treated the cases like puzzles, Grissom's hobby, and Miami is all about getting justice for the victims, the New York CSIs are just doing their job, the best they can.
I find that kind of refreshing, if not as indulgently enjoyably as Grissom's puzzles.