Short review:
-The plot feels rushed like "just accept this bunch of bs to keep things running", so don't expect good plot.
-The mc is as dumb and dense as always. At least he's not afraid of going for seggs, so that's a win I guess.
-I enjoyed the girls. Their personalities, designs and sex scenes are very different.
-The art was cool, classic korean light saber censorship. But personally I don't like the virginity blood that happened almost every time.
My takes:
I will start with the strong critique. As other have commented, it is bad the decision to tell most of the story through flashbacks during the sex scenes. Each day the mc gets one different girl and the interruption happens every single time, and sometimes it interrupts the sex scene several times. It would feel way better, both for the enjoyment of the sex scene and for the understanding of the plot, to show the flashbacks before or after it, instead of going back and forth. I guess the explanation is that the drug they consumed to get horny, also helps getting memories back and the mc had some level of alzheimer. Still bad story telling method.
After finishing the read, I feel like more is needed. The chapters focus too much in the experiment week and how the characters knew the mc in the flashbacks. There is a clear conclusion for that, but it doesn't tell you clearly what they will do with their relashionship afterwards. It seems like the mc will end with only one girl, but keep the others at least in good terms. But since there is a harem tag, I thought the entire point of this manhwa was to build up for all of them to be together after the experiment. The explanation of the author in the extra chapter doesn't give me that idea though, so maybe I just expected something that it wasn't the plan to begin with.