A 'great + unique' manga. At first I thought of neglecting this one (glad I didn't), but due to boredom at that time, I decided to re-read this. After 2 volumes, got attached to this and read it till the end.
The problem why some people have hard time in starting this manga I think is because of the sudden world introduction. Though, the world setting was explained bits by bits (and nicely), it was pretty much forced at the beginning. The result is that, it feels like being introduced to non-sense alien world. I believe many readers lose interest in first few chapters for this reason. (Second is due to art-style)
The plot base is heavy, but the author way of plot development make it easy to understand. Plot twist is interesting (though not the best) and can be deep at times. Lack of romance, though I feels that this element is not really necessary in this manga, as the rest is covered with good plot development and battles. This manga can be heart-warming for some readers (I cried once). Most characters are likable. Character development are carried well for most characters, as story goes, I'll find myself attached to more and more character. Author logistical error (mistakes unexpected by author) are very few, not to mentioned they are hardly noticeable (except if you pay very-very great details here and there). In addition, wild elements (elements not exist in the original literature) injected to the original literature are well planned and adapted. If you can accept the first 2 volume well, then you will have not much complaints regarding the wild elements.
For overall, the author did a great job in this manga. The manga is at overall neat, humorous, and interesting. One of the very few manga I would give score 10/10. To read or not, depends highly from the reader preference. But those that seek plot with mild entertainment would like this manga.