DO NOT MAKE THIS MISTAKE: You need to read "Sora to Hara" BEFORE reading O.B. otherwise you'll end up like myself and some others confused as to who these new characters are.
Occupation To Beloved is a continuation/epilogue of sorts for not just Kusakabe and Sajou, but many of the side characters as well. What always keeps me coming back to the series is the realism it treats to the fact these characters are gay. All these small moments like talking about sexual orientation with a classmate, or how a family member can lovingly expect their sexuality or for the family of another character not so much. They're instances that previous made me fall in love with the series and they are still to be found here in O.B. which certainly I couldn't be happier about. (Seriously though, I can't think of another BL that has a casual conversation about coming out.)
As far as the main two characters, we at long last get a glimpse of the couple as they maintain university and work, and a long distance relationship. I especially liked the portrayal of Sajou's growth. He was discribed as someone not particularly popular and in Sotsugousei his mom already mentioned he was smiling more for the first time in a long while. But the positive effects Kusakabe has had on him really shine through, and together they still make subtle yet significant steps forward.
While Kusakabe and Sajou are the highlights with their steady development and heartwarming interactions, this time we also get to see different sides of love through other characters. We can wish to have love as sweet as those two, but life isn't always so nice. From Koma's rather toxic ex boyfriend (a precaution if you're someone who would find seeing that unpleasant) to Arisaka's feelings of guilt towards his ex wife and kid, O.B. encompasses a wider snapshot of life and love. I think O.B. succeeds better in that regard rather than the traditional sequel you'd expect. Unrequited middle school love, relationships with bad people you met at a gay bar, dating the opposite sex out of social pressures; you wouldn't be able to see those different takes on the gay experience with just the main duo.
Lastly, the one negative aspect is the panels/page layout. Some chapters switch back and forth from past to present. Not a bad thematic devise, but it's hard to catch the change and made more sense after a reread. And perhaps it's due to O.B. being more anthology-like and the fact we're past the adolescent days of high school, but the panel layouts seemed more flat and didn't strike me as much as before. They serve the job just fine but I started to miss the charm of that sometimes whimsical flow from the previous series.
I'd also complain how this left me wishing to see more of Kusakabe and Sajou, but now there's been several one-shots since and another current ongoing manga to fill that void instead.