Well, first I have to say it was tough to decide on the poll between SR and WoD. While I love both, I classify them as WoD - present time gothic with mystical elements. SR4 is the dark future with cyberpunk, magic and various races blended.
The reason I like both is the rules are simple, the world is extensive and it doesn't have classes. You can write your background first and then build the character to match. The setting to me is just that a setting and a set of guidelines that can be augmented. I've played cyberpunk and enjoyed it but I didn't like the limitations of its world. I like magic and whatnot. However, cyberpunk had elements not found in SR, most notably rockerboys so I added to my SR game with conversions. Basically, I don't let the system limit my plots or the PCs backgrounds.