The Way Of The Warrior was a great action/adventure story but IMO it lacks the depth that marks all the really great Star Trek stories.
I wouldn't put it quite this way, but I do agree in a sense. To me, what makes DS9 a great show overall is that it is constantly increasing its scope, adding layers of plot and characterization, building on what it has accomplished previously, while experimenting with new ideas and storylines. The show keeps doing this right up until the end: each season has its own identity and contributes something new to the overall canvas. At the same time, the show never forgets where it came from and is constantly revisiting themes, ideas and character points from the early seasons. Not everything works, obviously, but the show is percolating with ideas where most of TNG-era Trek is incredibly bland and formulaic.
So, I have problems with the idea that DS9 becomes a great show with The Way of the Warrior. This episode does bring some important new elements to the table: an increase in scope and a new level of epic action. But at the same time, if the rest of DS9 were like The Way of the Warrior, and if the show had dropped the themes and ideas of the early seasons from this point forward, it would not be the great show that it is. TWotW is an important piece of the puzzle, but only one piece among many important pieces.