I did see the larger group one, how does the game work as opposed to the smaller group? It said the larger one is "scripted", but since I've never done one I wasn't sure of the difference. I would love to hear your experiences with the mysteries when you get a chance.
A scripted murder mystery is exactly what it sounds like. There's a basic script including dialog the guests/actors play out. The script is broken up into rounds each with instructions of what to do. That is the large group mystery.
I believe "Death of a Vampire (large group)" has 8 or 9 characters who follow the script with the rest of the party watching and asking questions.
The smaller group mystery is a "clue's based mystery". Each guest receives their role, a small booklet explaining about the other guests and a secret booklet almost like a dossier known only to them. Each guest asks other guests questions based on that dossier. At the end, each guest explains who they think committed the murder.
The website explains it much better than I could.
As to my personal experience, I hosted a Murder Mystery Halloween party last year. It was a clue-based party called "The Immortal Murders". Great atmosphere, and folks had a lot of fun with their costumes and roles. But that's about the end of the murder mystery part. People got in their roles, but they acted like party guests than murder mystery participants.
The Immortal Murders - A Halloween Murder Mystery Party Game
Honestly, they're a blast. I held a murder mystery party several years ago called "Pasta, Passion, and Pistols". It was scripted, but the fun was recreating an Italian resturant atmosphere and having the guests dress as their assigned character.
Pasta, Passion and Pistols
Murder mysteries are great fun, but you have to know your guests. Personally, I love the murder mystery parties. It's fun assigning the roles and having people get into it.
I say go for it, but understand things don't go as smoothly as the instructions indicate. "The Immortal Murders" was way to complicated for my party. Didn't matter as we had a ball.
Some photos from last year's "The Immortal Murders":
http://i166.photobucket.com/albums/u90/ThAnswr/P1040300-1.jpg
http://i166.photobucket.com/albums/u90/ThAnswr/100_1752.jpg
http://i166.photobucket.com/albums/u90/ThAnswr/Gang-1.jpg