This is one of the greatest epic love story of all time!
The immersion factor of the love story is wonderful, and the 'feeling' of love is pretty darn real, someone unique not found in most love stories.
Feel free to email me @ firstname.lastname@example.org if anyone has more information on the rational behind the epic love story / plot in MYTH. It'd like to hear an enlightened perspective on why the movie ended the way it did. Jackie Chan's own website doesn't go into the philosophical aspects of the love epic and I find that a little disappointing, since I would have to either figure it out on my own, or seek other people's opinions.
In particular, even if the Jack was a reincarnated version of General Meng Yi, why would Princess/Concubine Ok-soo not follow him out of the collapsing cave? I could understand her reasoning that its not the `actual' person General Meng Yi, but it IS his soul, so in essence it's still Meng Yi, because there is no other in the universe that is or could ever be more like the original Meng Yi. And since Ok-soo somehow has the dedication and conviction to persevere for all eternity waiting for him, it would seem silly that she would have found him (his soul, and thus the `essence' of Meng Yi) at long last and refuse to go with him. So she kept her promise until the end, waiting for the Meng Yi she now knows will never come, and gets here original wish of death 2000 years later being crushed by falling rocks inside a massive cave.
Or maybe Meng Yi did keep his promise. For the short period of time that Meng Yi spends with Ok-soo alone in the cave, perhaps Meng Yi used Jack's physical body in order to finally be with Ok-soo again? Maybe the whole reason Jack gets all these weird dreams was because Meng Yi had to keep his promise to Ok-soo, and he had chosen Jack to be the medium to use his body to get to Ok-soo. So in that case Jack is not the Meng Yi reincarnated at all, but rather the spirit of Meng Yi has temporality usurped Jacks body so that two could be together for a short while. So they both kept their promise. Ok-soo waited for Meng Yi for 2000 years. (Personally I applaud both Ok-soo and that soldier protecting her inside to cave for not screwing around with each other, cause 2000 years inside a damn cave with nothing to do can get quite frustrating, but I guess after about the first 200 years they got used to it) Meng Yi's general kept his promise. And Meng Yi himself kept his promise too, he did come back, he just didn't specify for how long.
They (Ming Yi and Ok-soo) lived a lifetime in the few moments they had together before Meng Yi's spirit disintegrated back into the death of which he came from, and Ok-soo and the Qin era soldier died in the caves. In the end this is what would have happened had Ming Yi not have been killed on the battlefield that fateful day 2000 years ago. He and Ok-soo would have been together, be happy and in love, and eventually they would have both died, except it turned out to be prolonged for two millenniums and the happily ever after stage was cut short. But they got what they wanted. So good story.