10 Reasons Deep Space Nine Is Secretly The Best Star Trek
1. It Calls Out The Federation
The reason that the fandom universally agrees the show becomes legendary in season 4? because season 4 is when the Dominion show up, and it and season 5 are when the show takes FULL advantage of Gene Roddenberry no longer looking over its shoulders.
One of the largest albatrosses hanging around the franchise's neck is that the Federation, when you actually stop and think about it for more than a second, is REALLY f*cked up! Picard and Kirk's missions in their respective shows were mainly about exploration and knowledge, this is true, but from a certain angle, it's also basically Manifest Destiny 2: Let's Enslave Space! Anyone with an eye for detail and even a basic education in social studies can see that the Federation - even without that subtext - is nowhere near as moral and upright as it makes itself appear.
That might be one of the reasons why Roddenberry was so adamant about the Federation never going to war in the shows he oversaw (another rule DS9 broke with impunity). Once the Federation got into a huge fight, DS9 was very quick to show the cracks in the entire operation. It spends an entire season calling out the Federation for its hypocrisies and "my way or the highway" attitude to other people's cultures.
And that is - above all other reasons - why Deep Space Nine is the best Star Trek show ever made.