I watch the original "CSI" as well as "Miami". David Caruso is actually the main reason I watch "Miami". I don't find him overdramatic. His line deliveries don't bother me at all, and if anything, I find Horatio is often understated -- he never raises his voice, with the tone of his voice often belying his words. His supporting characters, however, are not as interesting and fleshed out as on "CSI".
That being said, 2 "CSI" shows are enough for me. Don't care for the cast of "CSI: NY" either.