The general "giant dick (that may be thicker than the arm of most girls
)" MC who has - experienced or not - the skills of a reincarnated sex deity trope. Yes, porn game + self-insert/sex power-fantasy is a thing, but it takes the whole lewdness quite a bit over the top. Especially if the LIs turn into half-addicts because of it. It is not dealbreaker or so, just a eyeroll-moment from time to time.
The odd (lack) of balance between story and # of sex scenes: I don't think it happens THAT often, but I've seen a few games that have an interesting premisse and plot and you get "spammed" with lewd scenes that happen out of the blue (like an erotic "jump scare" XD); or where the MC turns of the brain and lets his oversized dick do the thinking as soon as he is offered a lewd reward in exchange, despite him being cautious a couple of text lines before. Of course, plot-driven character stupidity is generally not a novelty. The scenes itself are usually hot, don't get me wrong here, but I've reached a "point" where I read Visual Novels mostly for characters and sugary-sweet couple time (at least in jp. VNs, also called "moe trash" by avid haters
) and skip the sex scenes after maybe the first. So call me the odd one!