Story -7/10
QQ stands out from other harem mangas with the unique setup of each member being a quintuplet. For around 3/4 of the manga, story is very well written, to the point where id give it an 8-9/10. Each tuplet, (except for one, see later) gets a detailed character arc(s) and development with the MC. There is no obvious "main girl", the author does a good job stringing the reader along across multiple routes. Dialogue is detailed and varied.

Characters -8/10
This is where QQ shines, in my eyes. Each sister (except for one) has flaws, issues, yet is helped and develops with the MC along their own arcs. Each one is entertaining and unique, there is a type for every reader. MC is unique, not your average amazing nice guy like most of this type of manga.

Art-9/10
Art is excellent, from character design, drawing, and panel layout.

Caveat:
Savor the journey, as the end is controversial at the very least. One of the sisters, the quint chosen in the end, just doesnt get enough development. QQ is 122 chapters as to the very similar Nisekoi's 220+. It feels... rushed and not genuine. The MC's relationship with the chosen quint just isnt believable, so much to the point that even fans of that quint are upset. Honestly, any other of the 4/5 quints would be more believable.

Overall-7/10
This manga had a huge amount of potential and was great for most of its publishing. The journey itself is 9/10, and definitely worth a read. Just prepare yourself for the ending