A series like Super Robot Wars is pretty much made to appeal to fans of the Humongous Mecha genre. As such, the mere inclusion of a fan's favorite show since they were a kid is enough to cause rejoicing.
The release of the second trailer reveals the eponymous Tengen Toppa Gurren Lagann. As expected, fans are excited, since the unit will be a full-fledged one, rather than like the Arc Gurren Lagann in Saisei-hen where it's only available in an attack. Either Banpresto is rectifying this or something else the size of a galaxy (aside from the Anti-Spiral's Evil Counterpart of the titular unit) is dangerous enough to have the Tengen Toppa Gurren Lagann as a playable unit.
Likewise, the Endless Frontier EXCEED sequel didn't seem to attract much hype, as the only new characters are Aledy Naash and Neige Hausen (the former being yet another blatant Expy of an SRW protagonist). Once Axel, Alfimi and Fighter Roar were seen in the trailers.....yeah (despite Roar being a support character than a fully playable one).
One of the follow-up EXCEED trailers showcased the antagonists and the Big Bad, the latter who beared a resemblance to Wodan Ymir. Even better, the same trailer highlighted that bosses from the previous game will join the party as part of the support line-up. Hell, even Saya gets a friggin' Combination Attack with Reiji and Xiaomu!
Much of the hype surrounding the Second Original Generation was the result of Unexpected Characters, to wit the rest of the Masou Kishin cast (sans Masaki Andoh, Shu Shirakawa and Lune Zoldark) finally make their appearance in main continuity via the events of Super Robot Wars EX, after an eleven-year absence from consoles since Alpha Gaiden. Bonus rejoicing when fans discovered the Masou Kishin units can gain their final attacks as an unlockable treat, despite violating canon, which adds to the unexpectedness.
A follow-up trailer reveals more attacks for Shu's Granzon, culminating with the NeoGranzon. Of course, as per his story from EX, this is mandatory, but to include the same code input that unlocks the Neo Granzon RIGHT OFF THE BAT IN A SECOND PLAYTHROUGH? YES.
When Masou Kishin: Coffin of the End was announced, the hype for the Masou Kishin series was already dying (and likely the reason why this installment is being billed as the Grand Finale). Cue the first magazine scans and the teaser trailer showing Shu being The Captain of a new battleship, a trashed Neo Granzon, Tytti Noorbuck using a mass-produced Regelior-AR instead of her Elemental Lord Gaddeath and AmaraBalshem, who wasn't Killed Off for Real and winds up in La Gias. All of a sudden, players who aren't necessarily Masou Kishin-centric are excited for this installment.