Let's skip over the whole morals debate, as obviously this manga is targeted at a niche audience. Besides, even morally ambiguous stories can be thrilling to read if the author actually does something with the plot spiciness.
Such is not the case here.
For me, the mediocrity of this manga manifests in several aspects that form a one big MEH:
1) The female lead is 27 years old, yet in terms of behavior/mentality, she's pretty much around 14. I'm so tired of this trope. You get the supposed adult/'onee-san' type FMC, and then you make her awkward/ditzy/anxious/'pure' and all that bullshit. Choppiri's heroine combines all of these tired tropes into one and is utterly uninspired.
2) The drama is bland too, and at times it's so badly forced down the reader's throat that you can't help but laugh. I think my drop-off point before picking this up again was around the beginning of camping trip. Possibly one of the biggest snoozefest story arcs I've read in a while.
3) The art isn't something to write home about either. When you get all of these bland aspects, at least elevating your series with some gorgeous panels/raunchier stuff might do the trick. Nah, nothing here either.
4) Character growth? Why would you even need that, amirite?
All in all, this is one big fat 4/10 and a total pain to finish without falling asleep.
For the older woman/younger guy romance trope, you can check 'Kimi No Okaasan Wo Boku Ni Kudasai'. More realistic female lead, A LOT of personal growth coming from the younger dude. An overall great series.
Another alternative that's steamier and way, way more dramatic, is 'Tramps Like Us'/'Kimi Wa Pet'.
Both of these approach the younger man/older woman relationship dynamic in a more interesting, deeper, more versatile way.
