Read this earlier in the year, so I'm just writing what I recall from memory. The manga's pretty interesting, and I think the setting is the strength of this series; a number of details seem fairly well thought out. Another good thing is that somehow it manages to draw out some emotions; after a few chapters I felt ready to go out and kill some giants myself, the passively defending humans be damned.
As Blue-kun stated the weak point is the art. It's not terrible, but nothing remarkable. The art looks rough, but it could just be the intended style (?). I also get the feeling that the art doesn't fully illustrate or bring to life the ideas the author has, particularly for the action scenes.
Definitely going to keep an eye out for further chapters, hopefully the humans don't all get wiped out
