The Wire is a series that treats a subject that is not that common, but say, that's already been treated in other series. Its great difference is the way it does so.
What The Wire is not is a drugs-version of 24. It is not The Shield in Baltimore.
What is really is, is a show that tries to be as close to reality as it can, by depicting how complex the life and characters of people that deal with this struggle that many American (and many other countries) cities face. Omar Little for example, always has this nor innocent nor guilty kind of game. The police officers (and chiefs), who sometimes would like to do real police work, but sometime have to let this idea go because their job sometimes disturbs the "more powerful".
This show treat many subjects in its 5 seasons: corruption, childhood in poverty, truth and lies in journals and politics... But the fact is, it really does it in its very own kind of way. David Simon does not give Manichean or absolute answers to the questions that the show underlines. It lets you do so if you want to. In this way, it's kinda normal that it's considered as an UFO (I dunno if you guys use this expression in America^^) of TV.
So no, this show is not for everyone, but I tell you what, if you can follow the show, it's totally worth it.
(Pardon my bad English, I'm French^^)