Some aspects of this film are quite compelling. It's got a great space-opera vibe going, and an interesting universe. Despite all the downsides, I managed to stay interested in the overall feel of the universe throughout the film. But the plot is full of decisions and events which haven't been motivated well and answers given before the question is asked. it's a bit like having a rough draft of three movies' worth of script cut down to fit into one, without rewriting any of it to fit the new format, or to make sense without the 2/3 of it which were cut.
The characters all change their minds too easily, and don't develop their personalities or motivations. They just do what the plot tells them to. Pivotal moments for several characters are never resolved at all --- but, the character acts like it's resolved and they just go on their merry way, doing whatever the situation demands with no psychology to back it up.
At one point, a monologue is shared by two characters who ought to have opposite opinions, but the monologue itself is all from one POV. (That technique could have been really interesting, to have the story told from multiple POV! I got excited by the opportunity, and then was disappointed; a great idea, poorly executed.)
The "bad guy" actually empathizes with the "good guy" for the duration of the monologue; but his main thing throughout the rest of the movie is that he's incapable of empathy for anyone at any time, including his wife and his brother.
Harlock knows the main character is a spy almost from the very beginning, and it's never explained how he knows --- he's just omniscient. Then, the spy plays his hand really early in the plot, and --- rather than killing or capturing him --- Harlock ignores him completely.
Harlock's dialogue in that moment is roughly, "Well, you might ruin my whole plan or whatever, but I'm just going to leave that up to you. How about I focus on saving your life instead of defending myself from you?" I guess Harlock knew he was destined to win, so he didn't need to do anything about it.
Continually, Harlock gives the main character special treatment --- as if he were shepherding his own son --- with no personal motivation whatsoever; it's just because he's the main character, and needs special treatment in order to continue being relevant to the story.