Like everyone else said, it would be a very good slice-of-life fantasy if there isn't a total creep stalking/coming onto Ran in every other chapter. It isn't even really about the age gap (since that can be remedied as long as the manga doesn't let them get together until she grows up or something). No, it's about him being a total creep and all-around horrible person.
Seriously, every chapter with him in it is such a chore and I am more than a bit squicked out by how he acts around her. (I mean, he even thinks she's underage! But does that stop him from always trying to get into her pants? Nope. Talk about a horrible person.)
The only consolation is that the art is fantastic and Jin is the most fun person to read about since, like, ever. Makoto also became enormously cute after his apology.
edit: OK, now that the manga is farther along, I can say with certainty that I do not, in any way, like the inclusion of pedophile stalker. While he does become a better person, he is ultimately given far too much of a free pass for the shit he has done in the past (and the shit he continues to do by coming on to Ran despite her being underage).
Furthermore, the fact that his death is presented as a sort of "martyr" moment is just really souring. It's a really cheap attempt to make a dislikeable character likeable and to force readers into accepting said character as a "good person" instead of as the gross creep he really is. It's a flimsy and lackluster way of writing a redemption narrative, basically.
It would've been far better if the mangaka had actually made the other characters (including Ran herself) more critical of Outarou's actions, and had Outarou slowly work to better himself (and stop molesting Ran) and actually, you know, redeem himself with good, old-fashioned character development instead of through a cheap plot device.
It's a shame because Outarou could've been a good character, with nice character development, but all of that is scrapped in favor of a hastily written deus ex machina that ultimately took away any depth he could have had.
The other aspects of the story are still enjoyable, however, and I still really like the mangaka's art and storytelling style. Makoto also continues to impress, and remains my single favorite character to date. I just wish Irie Aki had worked a bit harder at developing stalker-creep too. But I guess it's too late for that now.