We had a BLAST.
I had 9 people, 5 males 4 girls. I played, and I was the hostess, and it all worked out fine. We're between the ages 17-18 and I was a little worried that because this seemed to be designed for office groups we wouldn't fit it very well- but I was wrong! I was also playing with a lot of introverted people, and people after the initial awkward stage shifted into their characters (I found providing food at the start provided people with something to do! Everyone gathered around the food and started talking)
Of course, not everything went smoothly- it was my first ever party, and the first one (murder mystery, I mean) that everyone had been too. However, when things didn't go so well, it was all quite humerous and just added to the fun.
There were lots of different subplots that had everyone hooked and added to the excitment.
I would greatly encourage everyone to dress up, because it really helped to slip into your character when you were dressed up, and talking to others dressed up.
Another thing is I would make sure you talk well ahead with the Inspector about how to handle the dead body. Mine had some trouble.
Another thing I would add is consequences for referencing your booklets. We had some very curious souls ask people "was that in your confidential booklet?" Which not only took one out of the game, but also created an awkward moment for those trying to lie...
Also, I wouldn't hide the weapon cards if you're all in small areas (I was in 3 reasonably sized rooms in a house plus outside) because people see who has the weapon cards.
Another thing I would do is add in a rule where people can only SHOW their weapon cards to someone if they are actually going to murder someone, because we had issues where people showed their weapon cards to prove they didn't murder an individual (a funny story about that- but thats for another day!) and so that way it made it obvious who murdered the dead individual.
The entire party was intense! Everyone had such a blast. It went for 3.5 hours, but it could easily have gone on for a further hour, though by then the murderer would've probably become very clear. I'd try to allow a lot of time for the party to go into if the party still has life in it like ours did.
Here are some pictures from it! Here is our very own Enid! (who also won best dressed), Seymour and Marsha! (me) Please excuse the red eye.