I'm not sure on the specifics, but the scene with Solus and Varis seemed to show Solus getting an idea. He's watching Varis decide to deploy Black Rose and musing over how "dear grandson" is making the "right" kinds of decisions and coming up with justifications that'll impress the people to boot. Then he thinks about Black Rose a little deeper ... it kills silently ... it moves like a shadow. Then he considers the fate of The First, and how ever since the Flood of Light began over there, it's been causing effects over here. Mulling that over for half a second he wonders "What if they could synergize?" and then he excitedly walks away like, "Varis, I leave the rest to you! I'm off to the First!" It's hard to imagine that is not gonna be 50% (at least) of 4.5 going sideways.
I can try to lay out a few things to help you make your decision.
I bought the original Drakengard on a whim and it turned out to be a mediocre video game software-wise (Dynasty Warriors + Ace Combat with a dragon) but the characters stuck with me for years. At first, the main character is just a vengeful jerk and his dragon partner is an ally of convenience, they detest each other. And every member of the party has some severely screwed up backstory that's subtly touched on in a way you might miss it entirely. And I recall watching the ending(s) thinking, "If only this made as much sense as Evangelion."
So then NieR came out and I bought it on a whim and halfway through the game there's a story about a red dragon and I was like, "This sounds like the joke ending of Drakengard." and did some research, and what the hell is going on, the same guy headed both games and NieR literally branches off of Drakengard's joke ending, timeline wise ... because all of Yoko Taro's games are stand-alone but (if you look close) connected by a complex conspiracy map involving games, novellas, audio dramas, stage plays, and musicals for no good reason but the fun of it. So already I had a sense this dude was off, but in a novel and magnetic kind of way, lol.
Anyway, the OG Nier, too, is a pretty basic, mediocre video game ... but with wonderful art, music, characters, everything, and then the story breaks your heart. Then you play through the second half of the game again with some slight changes, but it's just coming back to finish the job and break your spirit, too. I openly cried several times during that game. So when Automata was announced, I eagerly told Gamer Escape I was going to review it. I couldn't wait to write a review like, "This game is objectively middling at best, but you have to drop your entire life and play it right now." but Yoko Taro threw me yet another curveball and it's just a fantastic video game all-around, really.
So here's the thing: Automata isn't that sad. It's emotional, but very dry emotional, and most of it's in the context of the late-game. However, it's beautiful is many ways, and deeply philosophical if you read into it. But it plays off a plot point of the OG NieR, so it will spoil the entire game if you do Automata first, just be aware of that. There are also some returning characters references, so I would highly, highly recommend at least watching a playthrough of NieR before doing Automata if you want the full experience. Still, all in all, for everything sad in Automata, there's something fun, or just weird, or interesting, or supremely messed up.
EDIT:
Re:Matoya // Big shrug. They even made her first word a blend of two voices, but was that just for effect? Is this where the "Y'shtola seeing with aether is an added burden on her spiritual vitality" brick drops? Is Matoya temporarily hosted in her body to prop her up? Is this how we lose Matoya? Or is Matoya just a title that lives on?
Re:Minfilia // Big shrug. She rode the Lifestream, shattered like glass, became one with Hydaelyn, and was then ejected from the Sea as a reincarnated Emissary. However she shows up is gonna be a "Sure, whatever, that makes sense." from me at this point. Let's see where this goes, lol. Maybe her journey here will help her be seen more sympathetically by fans after they made half the fanbase associate her with a million interruptions of the story to take a trip to Vesper Bay for a secure chit chat and help moving crates or whatever. They helped resuscitate the moogles' reputation, they can help Minfilia grow. (Literally and figuratively in this case.)