I like the tone of early DS9. Everything's relatively upbeat as you'd expect from a traditional Star Trek series but the ghosts of the Cardassian occupation keep cropping back up and giving everything, as you say, a dark undercurrent.
There's a quasi-sitcom tone for sure. Sisko's situation is inherently kind of funny - he wanted to quit Starfleet not long ago but now he's become a religious figure completely against his will and he's therefore more or less stuck on a really shitty broken-down space station, spending a good chunk of his time dealing with completely inane problems. No doubt Brooks' performance is utterly weird, but in the first few seasons I felt like he imbued Sisko with a degree of exasperation and thinly-veiled frustration, which endeared me to him a lot.
Enjoying the rewatch. I'm in a (very?) small minority, but I think the early seasons (s2 - s5, more or less) are the best, while the later Dominion War stuff gets very tedious very quickly, so it's always fun to revisit the initial episodes.