It's certainly one of those systems where either you like it or you don't. Like I said, I think for some it's really difficult to get into because the books are horrendously organized.
As for the wild die is that 4 is the base difficulty for mundane actions for mundane people. Wild Cards (characters and special NPCs) should have a better than normal chance at succeeding at mundane actions. Most actions for characters will have difficulties above 4 or will require a certain number of raises to succeed.
One thing I really like about SW is how adjustable it is. By default it is very lethal. We use a "knocked out" rule that prevents death our campaigns but have added an edge that allows for lethal strikes. I think it's one of the optional rules in the core book.