10/10 For sure, this manga has everything you need for light reading:
-Cute characters
-Likable protagonist and likable love interest
-No stupid fan service
-No annoying childhood friend/tsundere school president/idol fight for affection
-Interesting, albeit simplistic and shallow, puzzle arcs (I did say light reading)
-Well characterized and three dimensional supporting characters that aren't paper cut outs
-Villains that are easy to sympathize with rather than being evil for the sake of being evil
-Minimal use of stupid plot devices to fill in plot holes (not being 300 chapters long helps, obviously)
-Believable dialogue and minimal use of "manga logic"
-Most important of all: great art.
I can go on and on about how great this manga is, but there are a few weaknesses. It is a bit shallow. The hardcore seinen/psychological fan won't be too intrigued by what's going on here. The exposition is lacking, the setting feels a bit forced and almost all background information is given through flashbacks. There are a lot of missed opportunities, especially at the beginning, to emphasize the difference between those with and those without irises. (I can't really fault the manga too much because it was supposed to be a very short series with no plans for a long serialization.) It also isn't very dark, which by itself isn't a weakness per se, but genre fans generally like the dark stuff.
Despite all that I give it a 10/10. There are deep underlying themes within the story; character foils and recurring motifs add to the complexity of each member of the main cast. It's rare that I care about every single character connected to the main protagonist, but this mangaka has done it. The strength of the characters far outweigh the comparably miniscule complaints I have about this manga.
Everyone should give this series a try, at the very least read the first 2 arcs.