These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Broken Base: Older titles can be given a pass as developer Banpresto was still fine-tuning the primary aspects of the franchise, but modern entries have split fans apart due to a myriad of reasons, such as the cast lineup for an installment (removal of older series in favor of debuts), Scrappy Mechanics (squad-based systems) and questionable use of Fix Fic (Doomed by Canon is in effect when it wasn't before).
Demonic Spiders: Ghost X-9s in Alpha, the Katana clones in Endless Frontier, Dimensional Beasts in the Second Z, certain Elemental Machines throughout Masou Kishin
Ensemble Darkhorse: Sanger Zonvolt began as a sympathetic enemy and late-joining Sixth Ranger type in Alpha Gaiden, but was so popular among fans of the game he was brought back as a major character for Original Generation, as a main character for Alpha 2 and has a prominent role in Alpha 3, then being the representative for SRW in Project X Zone. Being one of, if not, THE biggest badass in the Banpresto multiverse helps.
The Ardygun family in W are wildly popular, as well. The fact that they have one of the most iconic Game Breaker mecha in the franchise helped a bit of their popularity (or really, W, in general). For a one-game-only continuity Nintendo DS SRW, it's so well-liked that a sizable part of the fanbase considered it the best installment to date.
Judgment is pretty popular for its original mechanical designs, main characters and for breaking traditions, especially among Western players, thanks to the Fan Translation.
While there are a plenty of favorites for the franchise's original characters, those appearing exclusively in Original Generation are better received, such as Kai Kitamura of the elite Aggressors and The School children, namely namely Latooni Subota and Ouka Nagisa.
A scene in the final episode of Divine Wars about the characters' facial reactions on Lefina Enfield in a Playboy Bunny outfit became a meme on its own, usually having them get surprised about other "WTF" scenes in media. This went recursive by reacting to the reaction panels of its "Gaijin Yonkoma" predecessor.
"Real Men Ride Each Other"
Never be surprised if you suddenly see Mist Rex inserted in newly announced SRW screenshots, be it a licensed series or not. He's just that hated, the Trolls are using him to agitate fans into thinking he's in the next title.
One that existed since Alpha, only to be brought back via Original Generation, is "Sore mo watashi da!" ("That was me as well!")
The current trio of Dancougar Nova, Macross Frontier, and Gundam SEED Destiny. Nova missed Operation Extend, but otherwise the three have been included in every traditional SRW since their introduction. While fans do enjoy seeing the writers revamp the plot of SEED Destiny, Dancougar Nova isn't very plot-intrusive for crossovers and Frontier is generally considered the worst of the three. The fact that Frontier and SEED Destiny are included in order to generate sales doesn't help matters.
Seinfeld Is Unfunny: Playing modern, better-polished and more-refined games in the series first is an excellent way to ruin the much more-primitive early entries. It's really hard to be motivated to get through the Excuse Plot of the Nintendo Hard original Super Robot Wars when there's little to no battle animations, the lacking of any ability to skip them, being able to choose how to react to an enemy attack when it happens (instead you have to make one choice for the whole party), etc.