You know what it is? I just realized what it is.
It's true that SF stories have always been dumb, but they've also always been slight little trivial, frivolous throwaway things. But this, this obviously has had some significant work put into it. The elaborate cutscenes, animations, and voice work, they're all signs of effort put into this mode. That effort and the presentation that results no longer qualifies it as just a dumb fun throwaway thing. I feel like they're taking this seriously, and that actually comes off as a net negative, like an inverse relationship between production value and enjoyment.
It puts the effort into the same category as what MK and Injustice have been doing, and it fails by comparison. It can't even be a simple dumb fun thing anymore, either. It's a dumb thing writ large and with a lot of money (but also 5 months late).