Paul Fricker has created an interesting little scenario here that provides adequate material for a fast-paced one shot. I ran it for four players in a little over 2 hours - so, maybe add another 30 minutes or an hour if you manage to gather enough players for the full six gangster crew.
The adventure riffs heavily on 'Reservoir Dogs' - suggesting, in fact, that this might be the other job mentioned by Joe Cabot in the films naming scene ("You're not Mr. Purple. Somebody from another job's Mr. Purple. You're Mr. Pink!"). The group of three to six men with shady backgrounds meet to complete a heist and then hole up at an abandoned warehouse waiting for a late night boat across the river. The adventure includes characters sheets for everyone, including backgrounds and motivations for players to work off. Enough dynamic exists in the setup to ensure that you can manage this with fewer than six players, but as GM you need to take some responsibility for the other characters that can't take part. Mister Red or Mister Purple can't just disappear - they need to have got lost somewhere along the way.
When the adventure gets weird, players get confused. You need to have a means to take players aside and communicate to them out of hearing range for everyone else. I found it worth get some notes written down before hand to communicate some basic things ("The book is blank" or "You hear someone crying from the back office"). You also need to reinforce some elements, people and objects, to make sure players feel a real impact when they go missing. Some reactions really worked here - with key twists still getting attention after we'd finished. One or two developments really stuck in the players minds.
While the adventure does have a strong connection with Cthulhu, it doesn't have enough of a connection with the system to mean that you have to absolutely use Call of Cthulhu. You could easily substitute in something else, losing the character sheets and keeping the background sheets. Absolute improvisation could certainly work, too.
If I had a reservation it would be that the pay-off does depend quite heavily on someone knowing the protagonist behind the whole adventure. I had a group with a familiarity of Cthulhu ranging from some to none - and I doubt anyone had heard of the character behind the events. In this instance it would seem a good idea to have an alternate ending that still takes advantage of the great twist, but doesn't specifically require knowledge of Mythos literature. I think it would still work as a generic spooky tale in this light.
In the end, two characters died, with the other two well on their way, bleeding out or hanging on by a thread. Even without direct involvement from mighty Mythos entities, Dockside Dogs continues the tradition of high character mortality.
Highly enjoyable and a very worthy cause.
[4 of 5 Stars!]