Shiki from Togainu no Chi - the man has nothing going for him outside of his sex drive. Also there's no actual plot besides constant sex and mindbreak. Doesn't help his role in other routes is minimal at best and despite having strong ties with two other LIs.
True End in sweet pool - the game only has one LI all none of his endings outside of red river were interesting. The game failed to make him interesting and Youji lowkey has more chemistry with Zenya and Makoto(neither of them have romantic endings).
Madarame from Slow Damage - N+C tried to recapture Shiki's vibes and did a bad job. Somehow this guy is even less relevant and could've been removed from the game entirely.
Kouichi and Maki from NO THANK YOU! - I usually like older LI and don't mind if they're morally grey, but both of those routes were boring. Both of them had no chemistry with MC and sex scenes were very forced, uncomfortable and repetitive.
Ango from Lkyt - somewhat similar problems to previous examples, but he was an interesting character at least. Too bad he kept mentioning
in the most inappropriate times.
Matsuda and Takara from Paradise - I enjoyed how both of those routes started, but after LIs did 180 on MC I couldn't help but sigh. Takara's route was supposed to be the True End, but it left me with more questions than answers.
Naruomi from Nie no Machi - the game's writing is overall not perfect, but the nosedive with this route was obvious. His personality was also strange and not explained properly. His fandisk route was even more unenjoyable.