A LOT of people speculated we would get the ghosts early and then the rest of Gen 3 later on because of how the Gen 2 babies in to the rest of Gen 2 worked. If anything, December makes sense considering how much earlier we got the babies at the end of December before Gen 2 in February. While the rare candy thing sounded like a good idea from this community to include in the event, it's not like Niantic hinted at it, nor are we not getting a bunch of candies already through the reduced buddy distance and double candies on everything just like last year. A lot of those complaints seem to be coming form people who hyped this up for themselves more than they should have.
Personally, months ago (before I made this PoGo specific reddit account) I hoped that we were going to get Gen 3 by Halloween for the new ghosts, and I'm soooo happy to see that is actually about to be true, and that they're being premiered on Halloween! I'm happy they're carrying over most of the things from the original event (just wished we were getting 4x distance on our buddies but 2x is fine). That Mimikyu hat is going to be the first new hat I actually like and will keep on my avatar, and that's my favorite looking Pikachu yet so I'll take them too even though I, like a lot of the people on here, was getting tired of the hatted Pikachus (also still need the Pikachu medal). Last year I wasn't aware an event was even going to happen, and when it started I was out of pokeballs, and I have no visible pokestops from my house so I couldn't do anything about it for the first couple days, but now I've got 300+ balls, as well as 3 incenses and 15 lure modules that I've been saving for Halloween. To top it off, they're including Houndour too who's one of my favorite Gen 2 pokemon next to Misdreavus who was already mandatory for Halloween. The timing is absolutely perfect for me too, we've got 2 weeks which made me think we weren't getting it until next week, but this extra week means it'll be happening during a Halloween concert that one of my favorite bands from years ago is playing at that I can lure up in-between sets. And actually, for me, while it would have been nice to have all of Gen 3, I would've hated if the rest of Gen 3 were to come out and take the emphasis away from the spooky Pokemon for Halloween.
TL;DR: I'm already loving everything about this Halloween more than last years (besides the buddy distance being 2x instead of 4x) which was my favorite event thus far.