I worked for a Halloween City a few years ago and I had a lot of fun. However, I think your experience will depend both on where you are and who you get as your management team. My store manager was awesome, but I've heard of nightmare managers who just don't care or are jerks. The jobs being that they are low paying and temporary usually leads to crappy, uncaring, and lazy co-workers. In my area, we get a good mix of trashy customers and super entitled customers that have a rather unique local flavor to them. I've always been amused at people who come from other areas of NJ to work in my area and go "WTF is up with people around here?"
The schedule shouldn't be that bad, but expect a lot of weekends and afternoon/evening shifts. Everyone is expected to do pretty much everything. You will get a lot of people trashing the store and trying to pull a lot of crap (trying to get discounts, returning used stuff, etc). If you really need the money you can probably pick up a lot of extra shifts, because people will not show up unless you get a really good core group. Also, don't be surprised if you're the ONLY actual haunter working there. I was so I tended to get stuck working the prop/décor section a lot.
I managed to actually get Halloween off, but I totally negotiated that up front with the manager. Considering that I showed up for every shift, came in every time I was called, and took shifts just walking in (I literally worked next door for my regular full time job so I would pretty much stop in all the time), he didn't give me crap about not being able to work Halloween. That includes working with a bad ankle in a cast after hurting myself a week before Halloween and not being able to stand (I was stuck as a cashier instead). I loved working there and would do it again, but only if I had the same guy as my manager.