This animation was unfortunate to me, while I don't have anything terrible to say (besides the blue fluids, it just doesn't work), it wasn't simply worth the time which I already expected when it took ~2 years for a single animation, and with the overhype people are bound to be disappointed.
First thing is that the WIPs genuinely ruined for me, the animation that we got wasn't that different for what we already saw, just a more viewable experience if that makes sense, and the effect is much worse when is done to a long animation that took that much time, it's like watching a trailer for an episode that shows all the good parts, tho I admit that one is more on me.
Second, it's clear that they overshoot this one, it really feels like the animation could have been 10-15min without losing it much, their Mona x Slime one had a perfect pacing for its run time.
About the VA, I didn't really have that much of an issue like other people, but I admit that was kinda underwhelming when they keep mention multiple retakes and things like that.
At the end of the day it's still a good piece of animation, I doubt they're going to do something that long ever again and for good reasons, but I hope Mona x Fischl x Slime happens any time into the future.
In other words, I'm envious of people who just saw this drop of nowhere without being aware of how much time it took and no prior knowledge about it, lol