The first thing that guarantees the commercial success of a FG is a clear and easy-to-understand gameplay. (Easy-to-understand =\= easy-to-play)
Easy-to-understand gameplay means that the gameplay can be understood with as few external helps (going to forum, reading frame data, etc) as possible.
AC is on the right track to that. Some examples:
Every scrub knows that Slayer's BBU (236D) is hugely powerful and dangerous, just look at the move, no need to read the frame data to know that it hits really hard. Every scrub also knows how deadly Slayer's Dead On Time (superman punch that goes through the opponent if blocked) is, no external assistance needed. Every scrub knows what to do with Eddie's Shadow K (the 2-hit one which pulls the opponent in), it's easy to understand. Every scrub knows that Ky's lightning strike (after Vapor Thrust) is the thing to do if awesome combos are desired (it clearly looks like an essential move in combos).
Also, less and less obscure things like Slayer's backdash cancel (it was really powerful and important in #Reload, but not anymore in AC).