To Love Ru and I have always had a sort of love/hate relationship. The artwork is outstanding (especially the girls), I love the fanservice, I love the ecchi, and I even love the plot behind the story. And, by all that is holy, I absolutely adore most of the female cast.
That being said, there are a number of things I also don't like about it.
The main story is this: Rito Yuuki is a down on his luck teenager who can't confess to the girl he loves. While moping in the bath after another unsuccessful attempt at confessing his feelings, a very beautiful and very naked girl appears in his tub. Her name is Lala Satalin Deviluke, and she is the Princess to the planet of Deviluke and the daughter of the man who conquered the galaxy. After unknowingly enacting a Devilukean marriage proposal (apparently, the fondling of ones breasts is a time honored way of proposing on Deviluke for, well, reasons. MASSIVE PLOT reasons, you understand), and getting chased down by a bunch of aliens, he finds himself engaged. Now he's got to marry Lala, while keeping all of her other suitors away, or Lala's father will destroy the earth.
The story itself is actually kind of interesting for a story that is really nothing more than a massive excuse for ecchi and fanservice. It keeps your attention, it's funny, and the fact that every girl is stupidly attractive doesn't hurt.
Each females personality, despite being derived from a standard anime harem archetype, is interesting enough that you actually learn to really like the characters. There are favorites, of course. Mine are Lala, the upbeat and naive princess with a penchant for inventions that never seem to work right, and Golden Darkness aka Yami-chan, the kuudere assassin with the ability to change her body parts into various pieces of weaponry and hates perverts. All of the female cast is incredibly interesting and varied.
I also enjoyed how they managed to give every character a specific personality. In most harem anime, the female characters all blend together, and it becomes hard to tell who is who because they all act the same. Not so in this one. Every girl acts different, and that keeps things from getting stagnant.
However, while the girls are terribly interesting to the point where I wish the anime was longer, there is one major problem. Rito Yuuki. When the anime first starts, Rito has the worst case of the tropes Cannot Talk to Woman, Cannot Spit it Out, and Allergic to Love that I have ever seen. Any time he even thinks of a girl, he turns all kinds of red and starts sputtering nonsensical crap like the virgin he is. And that's fine. At the beginning of any story, the MC isn't supposed to be some kind of prince charming, unless that's what you're going for. Most characters are meant to start off from modest beginnings and become built up over time.
Just look at Luke Skywalker. He started as a fucking moisture farmer living with his aunt and uncle. Now he's one of the greatest BAMFs of the Star Wars universe.
However, 26 episodes later, 60 if you include the OVAs, Motto: To Love Ru, and To Love Ru Darkness plus its OVAs, and Rito Yuuki has hardly changed at all. In fact, only two things seem to have really changed. The first, he doesn't get as embarrassed simply by standing next to a girl, though he still becomes a stuttering, bumbling idiot without a single lick of common sense when something ecchi happens to him and whatever female is in his path at the time. Second, he did sort of, kind of, confess to Lala at the end of Motto: To Love Ru. Too bad nothing ever came of it.
The main issue I have with Rito as a character are thus: after a year of perverted situations happening in which Rito would fall into some girls tits, or her crotch, or end up randomly naked with an equally randomly naked girl for no apparent reason, he still acts like he always does. It's like the creator of the series never heard of desensitization before. There is only so much nudity a person can see before it just becomes an everyday occurrence. Sort of like violence. With a year of this happening under his belt, Rito should be practically immune to what happens around him.
Now, I suspect the creator kept him the same for comedy purposes, which would be fine, except the comedy sort of fell flat after seeing Rito fall into some girls crotch, blush like mad, and then get bitch slapped, chased, or something else stupid happening to him for the one hundredth time. Things like that just get old. You can only watch so much of the same thing happening before you go "Oh, well, is anything else going to happen? Like, I don't know, something new and interesting maybe?" And that's how I felt.
Despite my dislike of how Rito never changes, the anime itself is pretty awesome. I just wish they had more of it, because the last anime, To Love Ru Darkness, has a very incomplete feel to it, like there were supposed to be more episodes, but they just stopped being produced for some reason.
On an overall scale, I would rate To Love Ru with a 8.75/10. There was a lot about it that I loved, but those few issues that I didn't keep it from being a 10/10. I would still recommend anyone who enjoys ecchi, fanservice, and massive PLOT to watch this series, especially the Darkness series, as it's much more, eh, mature, then the first To Love Ru and Motto: To Love Ru.