#1 Not enough crime
Raku Ichijou tries to be a regular teenager while attending high school, but he can never escape the fact that he’s the heir to his city’s leading Yakuza family. Even though he wants to live a normal life and pursue a normal career, his home is filled with loyal crooks who dote on their “future master”.

His life is shaken up even more when a new transfer student arrives from overseas—the blonde-haired Chitoge Kirisaki—and the two immediately start off on the wrong foot. Turns out that Chitoge is herself the unwilling heiress to a criminal syndicate and tensions between her and Raku’s families flare up. The only way to avoid all-out war is for the families to be united, so their parents force Chitoge and Raku to become a couple… even though they hate each other… and Raku already had a crush on someone else…
The criminal theme of the story is what really drew me to Nisekoi, making it very underwhelming how little it actually matters. Chitoge and Raku must pretend to be a couple so as not to arouse suspicion, but their respective families are rarely around to observe. The façade instead exists exclusively for their classmates and most of the relevant ones among those figure out the truth early on anyway. This saps a lot of the tension away from Nisekoi past the first 3 or so episodes, turning it instead into a fairly standard highschool romcom with a sparse few eccentricities.
#2 A boring harem
Since their relationship is technically faked, both Chitoge and Raku keep their respective options open and interact with other potential partners. This is most obvious with Raku, as a harem of other girls soon forms around him and begin competing for his interest. However, he and Chitoge also grow closer together over time and begin considering if they might actually have feelings for each other after all. Will they stay together or is Raku destined for any of the other girls who are into him?

The question of which girl ultimately wins is one that makes harem romances interesting and intense, as the fandom splits between different camps who hope for their best girl to win out. However, Chitoge is blatantly the poster character for the entire series and her only real competition is Raku’s long-time crush Onodera. The other girls are barely present in the story and quickly cease to be interesting after their introduction episodes.
Onodera and Chitoge don’t fare much better. Onodera is just a very plain character. She is a nice friend, always supportive and kind, very moe, but apprehensive about confessing to Raku for various reasons. She is an inoffensive character, but has so little going on that it was difficult to be invested in her. Meanwhile, Chitoge is a tsundere and goes through the usual motions for one. She at least has enough going on besides her romance with Raku to be an interesting character, which again just hopelessly tilts the story of Nisekoi in her favor.
#3 The lock and keys
During his childhood, Raku fell in love with a girl whose name and looks he has forgotten about. The two of them made a promise to get married and, to symbolize their love, Raku owns an intricate pendant with a lock to which the girl has the key. A plot device that baffles me just as much as it did when Love Hina used it.

The competition within Raku’s harem keeps coming back around to wondering who this childhood love might be, which you’d assume is entirely pointless after everybody involved forgot about it. Even then, it’s not like you’re bound by law to honor a promise you made when you were 5. These characters are grown up now and are falling in love and making decisions based on the people they are today. Finding out which girl Raku liked best 10 years ago shouldn’t matter in the slightest.
Nevertheless, Nisekoi keeps teasing this mystery and it soon turns out that multiple girls in Raku’s girl squad have an ornate key. You’d assume they could just try them out then, but the show keeps coming up with new schemes to delay that from happening, as that would end the story and Naoshi Komi needs to eat.