The Shield is definitely in my top 5 but the writing is far too inconsistent for me to compare it to The Wire. Some of the acting is pretty weak too, and the characters aren't as interesting outside of a couple. Plus some episodes have a corny baddie of the week vibe.
All that being said it's a great show. S5 and S7 are god tier television.
The problem isn't uninteresting characters, the problem is the scope of the show changes and some characters are pushed into the background from season 5 onward. Dutch is one of the best characters of the show, Claudette is as well. Billings is the best form of comedic relief (bald middle aged detective if you forgot). Julian, Aceveda, and Danni are interesting characters that sorta stop being important after season 4.
The Shield is excellent at having a varied cast of characters and having each character used to maximum efficiency until the focus switches on the strike team.
The writing on The Shield is a lot more fun and entertaining compared to The Wire. The Wire's writing is top notch, very smart and very grounded, while The Shield has pulp and that pulp flows through most characters and performances throughout the show.
When it comes to The Wire, I find the majority of police stuff a lot less interesting than what happens on the streets.
