We played this murder party last New Years Eve, and found it hilarious. By the closing round we were all very imaginative and competitive about working out whodunnit. Clues were great, plot was easy to follow, DVD added to the detail and info. There are 3 golden rules I would suggest if you've never done one of these before...
1. Carefully match characters to guests - giving louder roles to more out going guests. (obvious but worth it, as you need someone not afraid to throw themselves into it to make everyone else relax into their roles).
2. Make sure everyone knows that they are supposed to dress and behave in character. - including accents... (again obvious, but do tell them it's expected and not optional. I guarantee that they will get so much more fun out of the experience if they have made an effort, and feel like they have done something different...but do remember to give guests plenty of notice so they can pull together a 'look' and perhaps go to charity shops for costumes...
3. Do make the effort to play this over dinner - it's much better than with a buffet or just drinks (which I've also done with other murder mystery party games - with much lesser results). Over the meal, you can relax from the spotlight, think up better padding for your story, take inspiration from other characters, think up questions for others, which all add to the success of the game.
A last thing - I would say that min age should be 11 - 12 yrs. Not because of content, but for ability to follow the threads of what is happening. We had a party with ages ; 8yr old (bit young - had to explain a bit on the way through, 11yrs, 21yrs, 30 something, 43yrs and 3 sixty somethings. Amazingly we were all highly entertained for hours. We're definately going to do another this Xmas holidays. Check out the 70's Disco party night set, that was great. I'm going to try the Poirot interactive DVD game aswell this year.
This is a game for 6 - 8 players