There are two major themes at play in this episode, or rather, one theme at work in two different ways. People don't have much love for those that are different from themselves. In the Star Trek universe humanity has mostly overcome racism and bigotry, so much so that even different alien species can live and work together. Chimera places the edges of that growth as a culture, as a species, in sharp relief.
The central players here are Odo and Kira with the rest of the cast playing one note versions of themselves to help drive the drama. Laas cuts right to the chase as he's too experienced to waste his time. Sisko and the gang are troubled by Laas for reasons they'd rather not face. There is a lot of "show don't tell" in the writing with just enough lay it out straight to properly frame the story. How Quark believably became this show's conscience is beyond me, but his role in this episode is pivotal as it saves the regulars from their limited points of view.
The other lens to view this episode through is one of self acceptance with undertones, both overt and subtle, of the difficulties faced by those who feel homosexual love. This angle is made even more potent once you realize Odo has unknowingly infected Laas the morphogenic virus he carries. But the episode never feels preachy. The Odo/Laas relationship and Odo's internal conflicts feel genuine and relatable to anyone who feels out of place in this life.
We are all prisoners of our own experiences. And yet we all have the potential to be so much more than the sum of our parts. While Odo is torn over who he is and where he belongs, it is Kira that drives the episode's final act. The chemistry between Odo and Kira is never more evident than it is here, and it is that chemistry that really makes this episode work.
As much as I love TNG, character's didn't grow and change like this on that show. I could probably snarkily poke holes in this one if I tried but I just don't want to. Chimera is Odo's "Far Beyond The Stars" and its everything Star Trek ought to be.