Necessary Evil is, simply put, necessary DS9.
I'll get my coat.
It's essential viewing, and one of season two's best episodes. I'd even go so far to say that I'd push it all the way to five stars, and say it's one of DS9's top twenty episodes.
I just love it so much. I know that we've been used to Kira's terrorist history since DS9 started, and all the subsequent years since it went off air, which I may feel may influence our opinion of the episode. I don't think it gets in the way of Necessary Evil being a classic though. The scenes in the past are brilliantly done, and I love Odo piecing together things in the present. His confrontation with Kira is particularly strong, and left me open-mouthed.
The Rom stuff is silly but it's a miniscule part of the episode. Badly placed? I agree with that.