I was pleasantly surprised by it. Not nearly as funny as Answer the Call but I think, more than any other films in the franchise, this wasn't intending to be a comedy so much as a "Kids on Bikes"-esque adventure, and it's a solid entry in it. The pacing and plotting were all over the place, but then it's a Ghostbusters movie.
Honestly, I couldn't make it all the through my most recent re-watch of the original. There's a ton of things from 80's that don't hold up (merchandise-first cartoons, waterbeds, reaganomics, etc.) but adult comedy is probably the top of the list, and for however much Ghostbusters is inextricably linked to your child (certainly true for me!) it was distinctly an adult comedy from 80's (not as bad as some of the more explicitly raunchy comedies ala Revenge of the Nerds et. al. but probably worse than you remember if you haven't seen it in a good long while). But I'll be damned if every moment of fanservice in Afterlife didn't still hit me right in the feels. Watching Bill Murray effortlessly drop back into 100% classic Venkman (a character I came to loathe in my last re-watch) filled my heart with joy in ways I cannot begin to understand, let alone explain. Which makes it probably crass manipulation at best on the part of the film.
9/10 would recommend.
e: I'll echo that the full Deep Fake Egon was a little too much; if they had just kept it to a pair of spectral arms helping guide Phoebe it would have :chef's kiss: