If you have read any of Hitoshi Tomizawa's works you know that he rights some crazy stuff that holds a bunch of symbolism. That's basically how you would describe this series in particular.
Plot: So basically there are many universes beside our own, and in our universe there is a syndrome children are suffering from called "Liesel Syndrome" in which a child disappears into another universe. The M.I.L.K squad are a group commanded by Liesel ("Sis") herself and exist to help the children that are transported to these vast amount of universes. Well. That's all I got from the plot.
Art: The art is actually very steady and holds up nice. Unless you don't like this 'Moe' type of art style. Yet the aliens he makes are horrifying in their own right. They look like huge mutated insects of some sort.
Characters: I could barely take something away from these children. They were all given a trait of some sort and were stuck with it.
You can barely remember their personalities.
Enjoyment: I enjoyed it a whole lot since I am a fan of Tomizawa's works including his most famous work: 'Alien 9'. But if you don't want to be mindfucked then you might want to drop this series now.
Overall: It was a psychological horror about poor children having to deal with horrifying creatures. When reading this series you'll get very confused and get surprised. The symbolism just clutters up and it gets very confusing and messy.
If you enjoyed this you should check out Tomizawa's other work 'Alien 9'. Instead it's a trio of cute girls dealing with aliens again with vast amounts with yuri undertones.