I like the open house idea. I find that many people don't want to commit to an entire evening and are more likely to stop by if you keep it casual. "I'm holding a Halloween open house - stop by and grab a bite and a beer - anytime between 6:30 p.m. and 11:00 p.m." I did that one year and most people that dropped by ended up staying the whole time. If you want something more structured with games, contests, etc. maybe the block party idea would be best. In any event, I say party!