Don't get me wrong, I liked Omar a lot.
You don't think McNulty evolved from a loveable smartass top notch cop to a happy familly man only to turn into an idiotic ass during the 5th season?
He was kinda an ass the whole show
(but likable anyway). Maybe in the 5h season more than before, but he did risk his career/freedom just to put Marlo and his crew behind bars.