Queen Emeraldas is a manga that began publishing in 1978 and is an incomplete work. Therefore, no real ending exists and this seems to be a common trend with Matsumoto's most popular manga including Captain Harlock and Galaxy Express 999 (last published in 2005).
Queen Emeraldas follows the same episodic formula that Leiji fans should be used to by now. Emeraldas searches for something no one must know and occasionally offering help to a young boy who seeks to sail space.
The manga also contains a comedic one-shot titled Emeraldas VS Harlock that offers comedic relief to the readers. Leiji pokes fun of the famous captains along with cleverly poking fun at his past work (shoujo manga).
A word of warning: Much of the backstory in this manga has since been retconned in other stories such as GE999 and SSM - because of this there's no particular requirements to read this work.
Another thing to keep in mind: In the usual Leiji style this manga will leave you with more questions than answers regarding the mysterious heroine. This is probably done intentionally, but it can be kind of unsatisfying. It gives you something to debate about at least!
Also, the art is fantastic. Leiji's art is far superior than just about everyone doing manga in the 70s. Especially when compared to the childish art of Osamu Tezuka. Leiji's style is incredibly unique and you won't find it elsewhere. His manly designs and his slender and gorgeous women and entirely unique.
tl;dr: Read this if you want to see Emeraldas being badass. read more