Why is 18 ... remains a mystery

One can only guess that the bare breasts of Eva Green are the cause which again shows the US hypocrisy.
The rest is the usual slaughter - a sword blow and felt the 4-fold amount of blood splashing out of a body. Unlike 300 - that's all just average, tricks underground hero imperious attitudes which also guarantees at this time no one went to war and otherwise little action.
Very often not even recognizable really what happens - it was much better in the first part.
Overall, you will not miss anything if you have not seen.