When seen today, Homicide looks pretty dated and fairly normal. This, of course, was before NYPD Blue and the Shield came along with a more dark look at police work, and The Wire put us in the middle of all sides of crime. Comparison with The Wire is inevitable, given the creator and the city are the same: Homicide is far less demanding, yet (I'm going to get flamed for this ) almost more rewarding to the viewer.
The characters are the best part: We watched Giardello, Munch, Pembleton, Bayliss, Lewis, Kellerman and Howard rise and fall (Sometimes hard) over the seasons. Even characters at their worst (Crosetti's Lincoln fascination, Felton's marriage collapsing) seemed realistically annoying, like that guy you know at work. The first episode I ever watched was the end of a third season two parter, and I knew every character almost personally by the end of it.
Seasons 1-4 are excellent, with 1 being something of a masterpiece. 2 keeps up the pace, although is too short to really get an arc going. 3-4 have generally a 5/6 working episode ratio, and Kellerman was introduced fairly well.
5 is where writer ennui creeped in: Some episodes are touching, but the format and actors were obviously wearing thin. To shake things up, Falsone and Ballard were added in 6. Sadly, they were initially added in every scene as complete know-it-alls, though Falsone got easier to stand (Finnegan's Wake, par example). Episodes became overly soapy and preachy, and as you can probably see in the tropes page, the end of the Mahoney arc ruffled most fans' feathers. 7 is not a complete disaster (Esposito is excellent even if his character is silly), but definitely is not the show in its prime.