Gemini, from the first game, kills one of his allies for no reason when he could've easily helped her and defeated Mega Man. He also manipulates a boy with multiple personality disorder into helping him to blow up the entire planet and is revealed as the one who manipulated King Cepheus into destroying the AM Planet.
Each rendition of the main theme, Shooting Star, is amazing. And then it goes vocal in the third.
It was supposed to be sung by Sonia... but Capcom never got around to it due to unfortunately low sales. Luckily there's a well-dome Japanese fan version available for your listening pleasure on Youtube: Here it is.
The theme of Spade Magnes's stage is also widely hailed as the best stage music in the Star Force Series. It manages to be energetic and intense without being over the top. Considering the limits of the DS sound card, this is saying a lot.
Die for Our Ship: Many GeoxSonia fans despise Luna. In fanfics, she is usually bashed or treated like a spoiled brat. The fact that the anime turned her from a Tsundere to a Obsessed Fangirl with bits of Clingy Jealous Girl didn't help.
Queen Ophiuca. Look at her official art◊ closely and you will see what is unmistakeably an exotic dancer outfit in her design. Somebody's been feeling repressed of late, hmm?
Fake Balance: In the third game, Non-Elemental non-time-stopping cards get the most perks in single player mode. Despite not being able to capitalize on the Elemental Rock-Paper-Scissors, they are the only way the player can raise the Noise Gauge which powers the game's Super Mode. During a long boss fight, it is possible to jack the Noise Gauge all the way to its cap, allowing you to see the real potential of your Finalized form.
Oh lord, the Gemini Spark chapter of Star Force, between Pat and Geo. The first part of which is more or less Pat and Geo going on a date together and then Geo shyly and awkwardly asking Pat if he wanted to be "Brothers" afterwards.
Geo was extremely depressed over Ace's death.
Geo and Jack in 3. More a case of Foe Yay, it starts off with Geo trying to befriend Jack. Then Jack seems to start finally warming up to Geo after they hang out in swimsuits at the beach. Then after The Reveal, Jack spends the rest of the game obsessed with trying to kill Geo (not defeat, kill), only to fail utterly to stop Geo from ruining all his evil plans at the last moment... then within a few minutes, gives into Geo's will, leaves with his sister back to earth, and eventually works to save Geo's life after he's left out in space. And according to the credits images, does become at least friends with Geo.
Moe: Luna's Day in the Limelight episode two-fer consists of her trying to learn how to cook for Rockman. She finally gets it down (after a long string of failures), and presents it to Rockman only to find that her creation was ruined in the latest attack. Her pout is adorable.
Zack, thanks to the events of the start of the first game. He still suffers from it, but people have started to like him for his roles in the later games.
In the western fandom, Luna garners a large hatedom, largely due to being the unpopular choice for the series' Ship-to-Ship Combat (see Die for Our Ship) and the tendency of those with Shipping Goggles to oversimplify/downplay or misconstrue her Character Development. The rest of her haters are simply sick of the Tsundere archetype. This is averted in Japan, where she has as much popularity, if not more, than Sonia.
The SF1 games had levels that fell into the same rut that many other Nintendo DS games fell into early on, with level puzzles relying largely on Touch Screen gimmicks rather than button pressing.
The SF2 games did away with this at first except for the The Final Dungeon. Remember those sections where you get chased by Murian guards? If you touched them, you will initiate a minigame where you need to draw lines on the guard with the laggy touchscreen function. In less than 5 seconds. Otherwise, a fight ensues. They are rather tough with a lot of hitpoints. To make matters worse in order to even reach the Final Boss you need to sneak through those guards. Lose the Le Mu fight and you have to cross the dreaded section all over again.
Ship-to-Ship Combat: Between Geo/Luna and Geo/Sonia shippers, sometimes elevating to idiotic heights.
They Changed It, Now It Sucks: Well, it is Mega Man. One of the main issues the fandom had with the new series was the new battle system, which stripped out much of the logistic and strategic complexity of Battle Network in favor of gameplay that heavily relied on timing and reflexes. Its detractors refer to the new battle system as a watered-down imitation, while its fans have actually compared it to the reflex-based gameplay of the main series' timeline.
Fans weren't in particular sure whether they preferred classic SF-Mega with War Rock's head for a blaster or new SF3-Mega with a much more streamlined Arm Cannon.
One of the main reasons for SF2's not so good reception is due to straying too far from the core plot (no concern of space at all in contrast to the first and third games).
One major complaint against SF3 was how the modified battle system arbitrarily isolated some of the Battle Cards you drew each turn, especially the more powerful ones; this is almost universally recognized as a Scrappy Mechaninc because of how it interrupts combos and general cohesiveness.
They Wasted a Perfectly Good Plot: Part of the criticism for the series, particularly the second game, was that it never seemed like the writers were truly taking advantage of both the setting and the characters. Part this can be seen in how the second game was handled, where it focused more on zany and silly scenarios instead of advancing the overall plot much of the time and for having some retreaded moments from the original game. It also wasted Solo's story arc by never allowing him to grow as a character.
Viewer Gender Confusion: Pat (as in Patrick, not Patricia) is dressed in purple spandex, and wears a purple headband with long hair. His androgynous name was probably an intentional carryover from the Japanese version, where he was named Tsukasa, a common Japanese name for both genders. To further the point, the name Tsukasa is usually written in hiragana if it belongs to a girl, and kanji if it belongs to a boy. But Tsukasa Futaba Takes a Third Option and writes his name in katakana. In fact, there's fanart featuring him as a girl that was produced before the first game came out.
How long did it take YOU to realize that Ken Suther was a guy? No points if it took learning his name for you to get the memo.