... 'cause it's a guilty pleasure... and yet it's grade-A RAGE material.
As many have pointed out already, this manga starts off great. That's exactly the problem; it's deceivingly good at the beginning. It deteriorates a lot later on, but by then you're already hooked. You're gonna wish you weren't, so that you could drop it and be done with it, but you won't be able to, because by that point you will have developed certain expectations that you will demand to see happen (well, it's either that, or I'm just weak and can't bring myself to dropping it).
Alas, the mangaka knows damn well what every reader wants to see, and she's using a carrot-and-stick approach to us. It is only by then that you realize that the title of the manga is only there to mock you. This story's ending might prove to be good (at least we all hope so), but the development so far has been anything but that. It keeps promising good times ahead, only to disappoint everyone in the next chapter in the most irritating, nerve-bending way.
Now, regarding the characters... I'm going to mark this next part as a spoiler, but I really suggest that you read it anyway, because it will give you a pretty good idea of what you're about to get into; plus, I'm not spoiling much of the story, really.
First of all, there's Utsumi, the MC. Apart from the fact that he's a wimp, and dumber than a bag of hammers when it comes to anything romance-related, the guy is simply in denial of the fact that he has a penis, as well as all desires associated with it. Seriously. You could swear that he's a eunuch, and in fact he would be far better off as the MC of a manga about some Buddhist monks in Tibet or something. Now, I'm no stranger to shounen romance manga; I know that these "traits" of asexuality are more or less to be expected of male MCs. It's just that Utsumi is really THAT bad. In fact, the only worse MC I can think of is Haruto of Kimi No Iru Machi, and that speaks volumes.
Then, there's Yuki, the beauty on the cover, and as you may have guessed, our MC's (platonic) love interest. She's also about 90% of the reason I'm still reading this manga, because I took a liking to her right from the beginning. However, and it pains to say this, she's one of the very few characters I can recall in any manga I have read that actually have NEGATIVE (as in reverse) character development. She started off by being daring, strong-willed and determined; a woman who knows how to captivate the man she wants. But after she and Utsumi become a couple, she just happens to remember that she's carrying a huge traumatic experience from a past relationship that makes her feel extremely uncomfortable whenever Utsumi tries to man up for a change and become intimate with her. All of a sudden, all of the willingness and determination evaporate and what she's left with is tons of phobias and retarded decisions. It makes no sense... If you're such an emotional trainwreck under the surface, why bother seducing someone in the first place?
Finally, there's a bunch of other characters whose existence ranges from forgettable to annoying. The forgettable characters include the occasional girl that is after Utsumi's dick this month (that's right, this is a harem manga, much as it tries to prove the opposite), and the annoying ones include Yuki's brother and another guy called Tooru, among others (you'll see why, I won't spoil it here).
The story itself is like an unholy amalgam of shounen and shoujo romance, where all the bad tropes from both genres are put together and all the good ones are thrown away. It's like an over-dramatic soap opera set in a Japanese high school. If you're not into that sort of thing, save yourself a lot of time and don't ever pick this up.
I can't rate this higher than a 5. I guess it does have its merits, otherwise I wouldn't be still reading it, but seriously, it's only good if you feel like torturing yourself. The only reason I give it a 5 is because I admit that I'm a victim and I'm hooked to it. Maybe it'll be a lot more tolerable after it's complete and you can read it in one go, but right now, it's nothing but a weekly source of frustration. I'm pretty sure that when the story finally ends, I won't be saying "awww, what a nice ending"; I'll be more like "phew, glad it's finally over". No matter how good the ending might prove to be, all the preceding rage will be too much for it to leave a sweet aftertaste.