Luscinia, Visionary Villain, or a short-sighted, deluded and ultimately revenge-driven bitter man?
Ass Pull: Some viewers are viewing Sorush's survival, and subsequent return with his fleet for the final battle to be this. Really, did Ades conveniently forget where the 4th Fleet went all this time?
Sorush nothing: How did KAYVAN survive his fleet being practically vaporized?
Then there's Giselle's Hyper Awareness at the climax, where she conveniently realizes that the Grand Exile shares the same basic layout of the Ades battleship Impetus. This is especially bad, as it pretty much renders Alvis' presence during the Battleship Raid entirely moot.
Base-Breaking Character: Fam, herself. Some viewers find her unwavering optimism to be charming while others opine that she's selfish and obnoxious. The latter group basically considers her a Creator's Pet.
Fridge Brilliance: Fam Fan Fan's name, unlike most of the rest of the characters, isn't clearly from any real-world language (it looks vaguely Cantonese at best). Characters' nationalities and social groupings are indicated by having names in the same source language, and since Fam doesn't really know where she comes from, it's appropriate that her name doesn't fit in anywhere.
Fridge Logic: Oddly, Glacians don't have Russian names despite speaking Russian. Glacies is not even a Russian word; it's Italian.
Expected due to the primarily-female main cast, but it's hard not to invoke this, especially after episode 4. This scene ◊ from the same episode does not help.
Here's a line from Fam to Millia and Giselle at the end of episode 9.5 (a Recap Episode):
"Is there a secret between you two?"
Dian and her navigator Viola are heavily implied to be an item. Viola's jealousy whenever Fam gets "too close" to Dian is already indicative of this. Also, Dian at one point vouches to protect Viola, and in the last few scenes they are shown to be very close indeed.
Viola's jealousy is understandable, since Fam does tend to get rather affectionate with Dian at times.
Tear Jerker: Fam receiving the locket of Sadri, who is revealed to be her now-late grandfather. She breaks down in tears, knowing that she and he will never get to know each other and talk about her late parents.
Viewer Gender Confusion: Viewers who haven't watched the first series would most likely mistake Dio for a girl. Not that he has a more feminine look now or the fact that his seiyuu has always been a woman helps.
Will They or Won't They?: More like a case of "did they or didn't they," it's heavily implied in the finale that Claus and Lavie got together, based on their interactions, but nothing was directly stated.