I've always been fascinated by syncretic religions, especially the combination of two wildly different belief systems. Recently, I've been fascinated by Santeria after reconnecting with an old friend (a Dominican-American) and introduced to his grandmother, who was involved with Santeria in some capacity. On the same hand, I've also been recently replaying an old, classic video game (Gabriel Knight) which gives a very interesting and, as far as I can tell, well-researched background on the various strains of voodoo and vodoun of the French-African diaspora, and it doesn't take a genius to see there's a lot of similarity between these practices and Santeria.

I am coming at this from a position of almost complete ignorance, from a few wikipedia articles. Can someone please tell me the difference between these religions' strains? What do they focus on? What do they omit? What differing relation to the original African religions do they have?