usually Sigma version always have that extra content such as chpaters, trials, and characters. I think NGS2 is the best on the series. Some might disagree on me this but NGS2 is the series i enjoyed playing compare to any NG series.
anyways, i hope Team Ninja doesnt "throw in the towel" on this game and try to come up what they can improve.
*out of topic* I also noticed that NG3 is still has it's regular price tag. some games with low rating scores would've drop their price by now.