The biggest difference between the two releases is the color of the Succubus. The original is a better, but it's difficult to find since there weren't as many released the first time.
There's also technically six figures. The four you mentioned and variant clear Simon and Dracula with open mouth.
In reply to X
They were trying to fit all the Belmont weapons into the line, but it would cost too much to give them all to Simon. So they split them up amongst the other figures. Succubus comes with the axe. Dracula comes with the watch. Alucard comes with the wall meat, cross, and holy water. Simon comes with a candle, boomerang cross, knife, jar, sword, morningstar, and vampire killer.