Gurps Voodoo was nothing short of a revelation to me when it was released in 1995. I was already an old hand at RPGs and a long-time Gurps player to boot, but I was seriously getting bored of the same-old-same-old magic options. I wanted something more than a laundry list of the standard spells. It was a time in my life when I was desperate for something edgier, something different. I also wanted something that would work well in a modern secret magic setting.
I remember that Mage: The Ascension was still relatively young at the time and it definitely started to scratch that nascent itch. In fact, it may have helped me realize what I was looking for. But for some reason I never truly warmed to the system. It was was too vague and (for my twenty-something self) too out there. Ars Magica may have done the trick, but I was completely ignorant of its existence until much later. And despite being edgy and different, Stormbringer was was too flashy for my needs (and also much harder to adapt to Gurps).
Gurps Voodoo was exactly what I was looking for. For starters, it was an awesome secret history setting in its own right, focusing on urban and developing world themes. Assigning supernatural causes to the urban blight in places like my native Detroit, it became a natural extension of my Gurps Vampire: The Masquerade campaign.
But its treatment of magic was where Gurps Voodoo really shined. First off, its excellent introduction to Voodoo, Gnosticism, and western cabalistic magic kick-started my own interest in these topics. Next, it detailed rules for ghosts and spirits that indelibly shaped my approach to such things in all subsequent games that I have run, regardless of system. Finally, it presented ritual magic rules that are still some of the finest that I have ever seen. The system was later expanded in Gurps Spirits and (finally) carried forward into Gurps 4e with Gurps Thaumatology, but the I've always favored the original setting-specific presentation in Voodoo.
The flavor of magic in Gurps Voodoo comes from the ritual elements and typically subtle effects. Before a magician can even cast a spell, he must first prepare himself, the ritual area, and various material components. Next, the mage invokes the power of one or more spirits, calling them to him with ritual techniques for getting their attention. Once the spirits arrive, the magician must communicate the intended effect. Some degree of sacrifice is usually required to convince the spirits to intercede on the caster's behalf. Finally, the spirits must be explicitly dismissed lest they linger and cause mischief or outright harm.
The skills that governed the various rituals were, perhaps, a bit complicated. First, there was the basic Occultism and Ritual Magic skills. Then, there were Path skills that were limited by the character's Ritual Magic. Finally, each individual ritual was a technique (maneuver) that defaulted to one or more paths and could be improved directly with points. The system worked well in practice, as characters could either be generalists by buying up the base skills or specialize in a mere handful of rituals buying the techniques. My only complaint was that it was a little hard to explain to newcomers and that it confounded the various character generation pools that were mostly designed for the default Gurps magic system.
Rituals themselves were mostly focused on binding spirits, warding areas, and manipulating luck. But there were also rituals for dream travel/manipulation, curses, and (of course) making voodoo-style zombies. It wasn't too hard to invent new rituals and later supplements (Spirits and Thaumatology) would later add many others.
A ritual description defined only the basic effects. Characters had freedom to customize the rituals to increase the duration, affect multiple target, work over a larger area, or last for a longer period of time. Additionally, mages could gain a bonus to their roll by including extra material components, performing a great sacrifice, or making use of powerful ritual spaces. Doing away with essential components would similarly cause a penalty to the character's roll.
I still use this system (expanded with Gurps Thaumatology) in my current Knights of the Astral Sea game. I must confess, however, that the process of assembling modifiers for a spell no longer suits my GM style. These days, I mostly trust that the party ritualist is doing it properly. But I still love the narrative process of ritual magic. I had intended to present some alternate rules that would streamline the mechanics while keeping the essential Gurps Voodoo flavor. Alas, it is getting late and that will have to wait for another day.