'Rally Cry' does work best when combined with the other organised play modules for SR4, but does stand alone well enough to offer a great nights' play. The 'Missions' style of play is very well-executed idea, especially when used outside of convention play. The modules, this one included, are written very tightly with a keen eye to keeping the plot moving and reasonably achievable in a short time.
The overall plot for 'Rally Cry' is classic Shadowrun - it looks easy on the surface, but plenty can go wrong for a group that is not organised or lacks a grasp on the subtle. There are enough twists to keep a one-night module interesting and enough leeway for the 'runners to get creative and take the plot in a direction which interests them. There is the return of a few characters from previous 'Missions' in this season so opportunities exist for character development too.
The one stand-out section for me occurs at the rally, and was written such that I had to re-read it a couple of times to make sure that I hadn't jumped to the wrong conclusion (which I had). If you can get this to play in the same fashion in your game, the PCs will have a moment of pure, complete terror. Enjoy it.
Stylistically, this is a great addition to the Shadowrun line and should offer an enjoyable play experience. In the tradition of other 'Missions; modules there are lots of tips and design elements which make GMing a breeze.
[4 of 5 Stars!]