The real issue with ATC is that, whether due to a lack of faith from the production, or due to fan outcry, the movie just absolutely will not let you forget about the original movies, which is to the films detriment. Your not going to top the original, so just constantly calling back to it it just going to remind me I could be watching that instead. Which is a shame, because the movie in and of itself is fine, though not without it's own issues.
Beyond that, it's a lot more slapsticky than the original and relies a lot on cringe humor which I personally don't care for. I found the characters to be kinda bland aside from Holtzmann (who rocks) and Kevin (who is hilarious, but kinda steals the damn movie)
All that said, I liked ATC more than I did Afterlife, even disregarding how terribly they treated Egon's character. (Cool, my favorite ghostbuster is a deadbeat dad, that's awesome.)
So yeah, ATC, third best Ghostbusters movie.
Also I can't agree with GB2 being less dark than the original. Wee scottsman could easily watch the first Ghostbusters but found the subway scene in GB2 to be too intense. The heads on pikes was damn terrifying and generally the movie is a lot scarier and darker than the original, to the films benefit I think.