There are aspects of past events that I really liked... Having a forum-based game component is a must for me, though. It's easier to spend time hanging out, making new friends, playing silly forum games and still participating this way.
Towns 2 could be a piece of things once its more annoying quirks are ironed out. I couldn't really enjoy the fluff event there this summer, because every time I tried to play there, things went horribly, horribly wrong, even with the fixes coming down the line every few days. The idea behind the event was great, but the actual gameplay was frustrating. I also didn't feel like there was much chance for real interaction with others the way the in-flash games were set up.
I did love playing ghost hunters in ZOMG! (and trick-or-treating, caroling, and easter chick hunting there too, for that matter). Hunting for things, random scavenger hunt type things in flash spaces are a little more fun than repetitive standalone games that get old (like 4 million games of tic tac toe- fun at first, but awful after a while when you're trying for the big achievements).
The NPC interaction leading up to the Zurg invasion was a blast, and I liked that it incorporated both towns 1 and the forums.
I think the key, even if there is a flash-based component, is to make sure that there's an interactive forum part, too.
I have a weird nostalgia for the grunny event. Not because it was fun (it was infuriating), but because it turned into a war of attrition to get the darned stage 5. I got mine, but I don't view the process of getting that achievement as "fun." The whole thing just got so mean-spirited, and I think that's something to be avoided at all costs in the future. I finally had to make a thread about Hemingway just to keep people from being jerks in it (no one posted there but my IRL friends who were in on the joke). Apparently no one wants to discuss Hemingway during an event, just so you know.
Thanks for asking for input. Halloween is always my favorite thing on Gaia, and I'm looking forward to whatever gets put together!