Having watched all 5 series in a very short space of time (over the past 2 months)this might colour my review slightly, however as of writing I can safely say that there has never been anything better I have seen, and that probably extends to movies as well as previous television series.
In a programme of great, great characters (the list is endless, Omar, Avon, D'Angelo, Bubbles, Daniels, Bunk, Rawls - not exactly likeable but certainly brilliant, and of course Stinger Bell) Jimmy McNulty rises just about to the top - quite simply one of the best and most enjoyable characters you are likely to see.
'Multi-layered' is one of those descriptions that you read and often it doesn't mean that much, but is some critics attempt to sound intelligent, but in this case the definition is spot on. This can be viewed on so many levels and each series brings something different. The story regarding Bubbles in itself is a masterpiece, they could take out all his scenes from across the 5 series and put them into a film, and it would win oscars across the board. To an extent Omar's story runs parallel, and whilst this doesn't pull on the heart strings in quite the same way, it is still exceptional.
My only slight criticism would be the level dips slightly in my opinion in series 2 (although people do disagree with that, so maybe is just how I see it and how I loved the storyline and characters of series 1 and 3) but 3,4 and 5 are exceptional. In a very, very (very) sad way by the end these characters felt like your friends, and it was pretty emotional that last episode montage.
Before it was the Soprano's, which I loved and was fantastic, but ultimately it didn't sustain it too well over the whole period, and don't think it had the depth of the Wire and did focus on one character a lot more, even if Tony Soprano was one hell of a character. I certainly don't remember as feeling as 'involved' in that as with the wire.
Films I have seen since, even very good ones, have felt slightly odd and light - how can a film develop a character over 2 and a half hours in the way this has done over 60 hours. Impossible.
One word of warning, if you're expecting a Prison Break / 24 / Lost type series, you're in the wrong place. This isn't cliffhanger television, or popcorn television in the way those programmes (much as i enjoy the first 2, not seen lost) they are fun and enjoyable, but ultimately there is no real depth to them.
And another - pay this the attention it deserves, you need to sit and watch this properly, not be doing other things whilst its on, it requires, and deserves, your full concentration. You will be rewarded.
One tip - I needed subtitles for a lot of it, it does help.