After TNG played this game of an emigrant who takes the traditions of his own culture more seriously than the people who never went away, of Worf the hyper-honourable Klingon vs. all the scheming, Romulan-like Klingons, it was simply necessary to have a Klingon character who does not match either of these extremes.
That's true. It was past time for a Klingon who wasn't a stereotype. Martok was a well-rounded character, with a nice balance of all the Klingon traits. And he didn't struggle constantly with his identity, like Worf. And B'Elanna, for that matter.