There are a few things I think it does really well. The dialogue and writing in general is part of it. The writer channels part of herself into the characters and it comes off as being very genuine. The two Kims are both LGBT - Kim Q being transsexual and Kim D being bisexual; the writer is transsexual herself and began writing the book when she began transitioning. There are a lot of hijinks and overall the first series is a lot of fun, as opposed to the second one which is that and has a little more emotion behind it. Apart from that, there's a lot of clever world-building, because they have a blank-slate to create whatever kind of universe they want for the characters; the ideas that they present are interested and relatable.
Simply put, it's just a lot of fun to read the kind of space-faring hijinks these characters get into.