The Wire is slow burning. There's rarely any action, suspense, or "twists." The strongest part of The Wire, besides the acting, is the characters and how real to life the writing is. Unlike Heroes, The Wire does an amazing job of having the characters face consequences for their actions. You always mention TV being an art form, The Wire is probably one of the very few shows that can support that.
I too am on the 4th season, and it sometimes feel like a chore. When I first caught 24 and Supernatural on DVD I watched a season every two days. The Wire has taken me close to a year. It'll definitely be a monumental task and time consuming to review a show such as The Wire. Best of luck if you chose to.
Also, each season has a self-contained story (with exception of seasons 1 & 3 - they go together.) Still, the show has to be watched from the beginning because characters' actions carry on through the seasons.