These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Arc Fatigue: The childhood proposal mystery. Yes, the main plot. Over 100 chapters has gone by, and only a few details about it have been disclosed. That being said, the chapters that actually focus on the main plot are generally considered the best ones. The problem is that for each main story chapter there's at least five one shot chapters that serve little purpose beyond drawing out the manga.
Fan-Preferred Couple: Several fans, parly due to Arc Fatigue and frustration with ever-complicating harem hijinks, have expressed the desire for the story to focus more on Shuu/Ruri than any of the potential couplings of the main characters.
Hollywood Homely: People sometimes wonder how someone who looks like Raku could end up with girls like Chitoge. This trope is zig-zagged though, since it's revealed he was actually quite popular amongst the girls in middle school.
Idiot Plot: Chapter 52, where Raku has to find out Chitoge's measurements in order to open a briefcase. He figures that asking her upfront would label him as a pervert. So what does he do? He sneaks into the girl's room during their physicals, followed by disguising himself as a doctor to look at the charts. And when that all fails, he decides to finally ask her directly. By shouting it as loud as possible in a room filled with changing girls. It's even lampshaded by Raku himself at one point as he wonders why he decided to sneak into the girl's room in the first place.
Paula and Seishirou have a bit as well, though mainly Paula.
Marika's friend Mikage is described as being a "dirty old man" and is possibly an outright lesbian.** Haru's friend Fuu-Chan has some strong feelings for Haru. There is also Haru's slight obsession with becoming friends with Paula.
What an Idiot: Most of the times, Raku is an Accidental Pervert due to situations beyond his own control. This is not the case in Chapter 52, where he invites it upon himself after pulling one stupid antic after the other.
Woolseyism: Marika's proper speech is translated into English as a southern-US accent.