None of that makes these shows bad, mind. But DS9 is the only show where the characters really grow and change, where the character of the show in the beginning are no longer relevant in the end, where the setting itself has changed.
Hey now, Picard plays cards with his crew at the end.
But seriously, Picard and some of the other characters only really show some modicum of growth and depth in the films, aside from both subtle and hammy attempts with Data's quest to become more human.
I agree that the emotional crucible that most of the DS9 characters are filtered through is compelling and merciless and hints at Ronald D. Moore's later opus, Battlestar Galactica.
To be fair to TNG, it was essentially designed to be a "monster of the week" show while DS9 was deliberately or inevitably morphed into sweeping story and character arcs.
Some people out there like the episodic approach whereby they can watch virtually any TNG episode and not be bogged down by having to understand the ongoing storyline, much like a science-fiction version of Law and Order.
But I think there are more limited opportunities for drama and true emotional depth.
An episode like "Inner Light" from TNG is impressive as it manages to carry so much emotional heft in such a small amount of screentime - although it's basically just Picard for the entire episode.