I just got back from Birmingham UK where I demoed My Mom is a Witch on EGX. I had a double stand setup with two computers running the game. Four players could play on the left one, and two on the right one. The laptop in the middle just looped through the trailers all the time.
EGX is awesome for playtesting. The game logged the play stats in the background: 1682 player-sessions were played. We shared about 800 flyers to people who played the game, so everyone played about two games on average. Having two computers and multiplayer allowed a lot of people to try it. The event ran for four days, Saturday being the most crowded:
EGX was open a hour longer during the weekend days, but that additional hour didn't bring in many players. Here's the breakdown by the hour:
There were different categories of passes. From 10am to 11am only members of the press and players with super pass would come in, but they were mostly interested in AAA games, so it was rather quiet on all indie stands during that time. At 2pm there would be a huge influx of new visitors who had the afternoon pass, and when they browsed around and determined which games they want to play the interest for My Mom is a Witch would peak around 3pm.
My Mom is a Witch can be hard for beginners, so the average playing session took only 3 minutes and 21 seconds. Most of the players started a new game if they died quickly. Here's the breakdown of the sessions:
Action rougelikes are great for event like this because of the short lenght of a single game. Since play sessions are short many people can try the game. Contrast this to an RPG that might take 30-40 minutes to try out and get to the core. In total, we had about 49 hours of playing time spread across two computers and four days, making it an average of six hours of play time per computer per day.
I also tracked how far into the game would the players progress:
90% of the play sessions were long enough to experience the game properly. Almost half of games went deep enough to discover some of the cool content like the item/potion/pet shop, treasure room or the boss fight. Since most of the players played twice it means that everyone has seen at least something. Of course, the game is roguelike and you only get to try a subset of weapons, items and mechanics on each playthrough.
One of the goals for EGX was to get My Mom is a Witch through Greenlight. It was a failure in that regard.
For the first three days, we only got nine Greenlight votes. Saturday evening I did some major changes to the game. I added a revival timer for multiplayer games, which made the game more fun. Also, some I changed some of the controls to make it more intuitive to the players. This resulted in many happy faces and we got 30 votes that day. Still, going all the way to Birmingham to get 40 greenlight votes (or even 120 if we had a better build ready from the start) isn't really a good deal.
TL;DR: Greenlight marketing has to be done some other way.