I think it ramps up as it goes, although it always had more nudity than shows such as Rosario to Vampire right from the start.
Yeah, it continues to get more and more prevalent till the end of the first season, then the sequel show takes everything to a whole new level of fanservice (to the point that if you were watching the live version instead of the later released one you'd think you were watching a fireworks show with all the brightly colored censor lines filling the screen), and then continues to ramp up from there. That said it still doesn't come quite in line with the source manga, which started out with more, then also took another level of fanservice with the advent of TLR:Darkness. Let's just say that the Darkness writer and illustrator each take great joy in seeing just how close they can come to violating the Japanese censorship laws (there have actually been several petitions by various groups to get the work reclassified as hentai) and the manga illustrator has become very, very good at using tiny hidden reflections to show that, no, he isn't using the
Barbie Doll Anatomy Trope like many anime/manga do, his characters actually have stuff down below. You can bet that in Darkness for just about any prominently censored scene he's stuck a reflection of the goods hidden on a semi-reflective surface somewhere.
I kind of like that the protag of To Love Ru isn't completely hopeless. Aggravating as hell on occasion, but actually an okay character most of the time. The way he's handled some of the threats that have been thrown his way has been fairly convincing, but the way he handles his love life is pathetic and really smacks of a stupid high-schooler who's hung up on his 'perfect' girl and ignores the one right next to him. But the show knows damn well what it is, and doesn't pretend to be anything else, it's selling T&A, and that's all there is too it.
Or the 15 next to him by the current point in the manga.
In short, if you'd like to see (for reasons of your own, of course
) Just how close an ecchi fanservice series can get to being hentai then feel free to read/watch the whole thing. If you like wacky harem comedy, but don't like fanservice out the yin-yang, just watch the first series; don't go on to TLR:Darkness. And if you're the type of person who dislikes anything but the most subtle of fanservice, then don't go near either of the titles with a 10 foot stick, the main character is
the embodiment of the Accidental Pervert trope, to the point that even the in-story characters lampshade how ridiculous simple things like him falling over can become.