When i do a review it's because i have things i want to get out for me. I invested a lot of time into this manga since it's 21 volumes.

There are various things i didn't enjoy from this manga.

The most important: If part of your interest to read this manga is to check out the ecchi, let me tell you calling this ecchi is an insult to the genre. If you are going to draw people naked why delete the nipples? you take the luxury to draw voluptuous women for the cover but the most you show inside is a panty and a bra.
The "ecchi" is scarse, WEAK AS FUCK, literally just because you show a fully clothed female from a lower angle and she has big tits you can call that ecchi? that is cheap and effortless. And on top of that when there is something it's nothing the author hasn't shown before. So it's repetitive.
Terrible, terrible ecchi on those terms.

Don't expect to identify with any of this characters because the are pathetic.
This is common sense. If you google "lost in island show" you are probably going to get a ton of shows ,maybe you watched a few or know a few. What is the biggest threat in those shows? THE PEOPLE.
The whole school wakes up on an island without rules. What is the first thing the protagonist and his group do? trust absoutely and without question in the word of complete strangers they just met 1 minute ago. And because of that bad things happen.
Why does that bother me? first, it shows lack of common sense. Second, it's a repeated case throughout the manga. Like this group of kids have amnesia and are stupid.

Akira the protagonist is as big of a pussy as Rito from To love ru, this guy can't look a female showing interest for him to the face without blushing, or being oblivious. A curious case for this manga, since the author was so invested in painting him as a pervert watching secret recordings of his female classmates in bikinis and lewding over them but when it's time for action he suddenly becomes the biggest homosexual.

The weak females constantly slow down the group and cause unnecessary bad situations. Like i said before the author puts the characters in situations that lack common sense. In many ways this happens repeteadly.
Maybe if it didn't have this kind of things the ending wouldn't have been rushed.

I didn't like the fate suffered from actual useful characters compared to the fate of the worst scum characers.

It has a rushed open ending.

Wouldn't read again.