I feel the art (especially the faces), the comedy, and the sprinkle of mystery make this quite non-generic. This doesn't really feel like harem either—though I haven't read any harem manga to really compare this to—instead this reads like a love polygon.
Not to say this is some masterpiece of course, nowhere close.
To be honest, to me, it's a love triangle with additional hangers-on to the male lead. So far we only have one of the hangers-on who they fooled us into thinking she was a guy at first and a rival for Chitoge's attention, but that got rapidly shifted to her being a reluctant admirer of the male lead shortly after the revelation that she was a girl, with her mission and her feelings at odds.
There's more to come (based on my knowledge from watching the anime), but really the only two girls that really matter are Chitoge and Kosaki. One of the ones coming up makes a big show of things, but I just can't stand her. Her role is pretty apparent, though, I feel...
She's meant to be the one that ostensibly was the reason for the 'marriage' part of the promise that Raku remembers, and because she's just far too overbearing in her pursuit of that, she turns Raku off pretty badly, and thus that part of the remembered promise seems like it can be safely ignored.
Also, Seishirou seems to be partially replacing Chitoge's role as the tsundere as Chitoge gets less and less violently embarrassed at Raku and becomes more and more legitimately fond of him. There's another girl that helps to take on the 'crazy hatred' angle of a tsundere in addition to Seishirou (without the dere,
at least at first, I think?), but it'll be awhile for her to show up, I think.