When corpsec is raining lead down on your head, a wardrobe malfunction will get you dead. To survive against gangs, syndicates, and megacorps, shadowrunners need the best gear they can make, buy, or steal. Arsenal covers everything a runner team needs, from weapons and armor to advanced electronics and spy toys to the latest state-of-the-art drones. It also covers the intricacies of the black market and drug trade and provides advanced rules for combat and martial arts, mixing your own chemicals and explosives, and modifying your weapons and vehicles.
Basically, this is the equipment book everyone playing Shadowrun 4th edition has been waiting for. Guns, big guns, machine guns, taser guns, dart guns, weapon mounted guns, gyro mounted super guns attached to drones... can you tell it's got a lot of guns? This book has the killing power your runners will need.
So, what else does the book have? Vehicles and drones take up most of the rest of the book. There are dozens of neat drone designs and a good cross section of vehicle types. If you have a gear head or a rigger, then this books is a must have.
They've expanded the standard vehicle mod sections, and also given much better rules for weapon moding. There is a lot of mundane equipment, spy stuff and the like that can give you the edge you need in a fight.
Don't think that this book is useless for your mage types either. There are some really nice mage specific items, and the Adepts in your group will be very intrested in the Martial Arts rules in the back of the book. They give some very good options for the martial types.