6 episodes was definitely too long. Four would have perfect imo. Still, while its not my favorite entry in the Garo franchise, I had a fun time with this. Loved the return of the actual armor, and I can never truly dislike any Garo work that feature the horses, and yes that does include the Kiba Gaiden.
Zero was awesome as always, and seeing him give dramatic speeches about being a protector of the people reminds me of just how far the character has come from being the revenge driven jerk he was in Season 1. He doesn't really change much as a character, but I was fine with that since almost all the newer Garo works featuring the original cast are less about them growing as characters, and more about them reaffirming their character growth from Season 1 and becoming bastion of how Makai Knights/Priest should act to newer characters.
Yuna and Kain were okay. I think what they were trying to do with those two was give them shades of early S1 Rei, with Kain being a dick and Yuna's quest for revenge, but I really feel they needed a few more personal quirks to really make the characters feel more original. Between them and the barkeep, who I thought was fantastic, it really seemed they were trying to give Rei his own support team, similar to Kouga, but since Rei is by nature the loner, it felt very forced at times.
Ring was a pretty interesting bad guy and one we haven't had yet in the Garo universe, and I'd be interested to see another villain inspired by his ideals come to power for another short special. I found it funny though that the actor's acting was better in Japanese than English. Also, while he definitely had a great villainous presence I really feel when it came to the out of the suits fights, he was probably the weakest of the primary cast, especially whenever he and Zero clashed.
My biggest gripe with the show though was the young couple. Like what the point of them even? I really thought that during the scene where all the humans are beating on Rei they would at least have come to his defense, since you know he saved their lives, and prove that regular humans could be selfless as well, but they didn't, and when a show goes to out of its way to remind me how shitty people can be, without showing the other side of the coin, it really bugs me. What's worse is that they didn't give any resolution on what happened with the two of them!