Ever since reading Black Cat, I've followed Kentaro's art. He wrote a solid shonen story as well--nothing too deep or thought-provoking, but sufficient for its target audience (I was fourteen at time of reading).
Let's get the good points out of the way first:
The "plot" in Darkness is way beyond its predecessor, but more on that later. The art is good, too. Really good. Also, this may be the first time I've seen a manga approach a harem situation with a "bed ALL the girls" attitude, and coming from one of the girls, no less. Yes, the harem plan relates to the back story, but that's about as deep as the story gets.
And... that's about it. Now let's rip it apart.
I have no problem with episodic storytelling, but in Darkness, you can easily predict the ending of every last chapter: Rito is thrown into a sexual situation (uncensored this time), gets slapped/punched/kicked for his clumsiness (as he always "falls" into girls' chests, etc.), and ends up somehow attracting a harem of girls through being a nice guy, all the while never taking his existing relationship a step further.
His existing relationship was unexpected. Though it happened in the end of the manga, I'm genuinely surprised that Rito actually got a girlfriend. But now what does she get? One chapter? It seems almost as if they've grown farther apart.
The characters are all as shallow as you'd expect from a harem manga. The cast of girls is only attracted to Rito for his outstanding kindness. They never get any deeper than that. The first part of TLR and this are filled with moments that could potentially develop excellent characters, but unfortunately, the writer doesn't take any opportunities, instead leaving Rito as a wish-fulfillment self-insert character.
I mean, who else has noticed that Rito never does anything wrong? He gets kicked around a lot for accidentally touching girls, but it was never his fault. Nothing was ever his fault. Come to think of it, what flaws do any of the characters have? And I'm talking about real flaws, not hastily-added anger issues on top of a tsundere personality or anything like that. Everything is superficial at best.
All in all, To Love-Ru Darkness is a poorly-written, but extremely well-drawn manga. You may come away from this manga with a perverted smile remembering an excellent pseudo-sex scene, but if you're looking for deep story and characters, you won't find them here. I have to give props to the writer for daring to write what is potentially the first non-hentai true harem, but unless the later chapters get a lot better, this manga will forever live in mediocrity. Five stars out of five for the art. One out of five for the writing. I rate this a six.