I think the most important thing anyone should know before reading this manga is that it doesn't really ends. The 4 volumes encompass 2 story arcs and even though those stories are told to completion, the main plot is never resolved.
Crucially, the romance goes nowhere. It's a real let down to read the last chapter ever published and find all those dangling plot threads.

That said, let me nitpick a little:
* The art is nice, but the artist's narrative is really confusing, specially in fight scenes. It's made worse by the classic shoujo manga gimmick of going light on backgrounds/establishing shots, so that sometimes you can get really lost on what is happening and who's where.
* Lydia is a good character when she gets to act, too bad most of the time she's just wandering around wondering what is going on.
* Edgar is a very interesting character, but he's also a creep. I have never spent so much time screaming "it's a trap baby girl!" to a manga as I have whenever he'd go all romantic around Lydia.
* Raven is a narrative device, not a character. I guess he'd be fleshed out if the series took off, but, since it just ends, he ends up being The Thing Used To Save People and not having much of a personality. It makes me sad, since he's my kind of shoujo manga man.
* There is a serious lack of motivation to all characters. Protagonist or secondary, they all just seem to drift around and react.

To sum it up, I don't really recommend this series to anyone. It seems it's adapted from a series of light novels, so maybe if you watched the anime and want more you should go after the books. They're bound to better, right?