Two versions that do not like each other.
Our environments shape us to some extent, and to some extent we are shaped by the people around us, and to a small degree we have some innate core of self that interacts with the environment and people around us to create the person we are. In this case there are two very different environments, and those different environments combine with different versions of the same friends as they wrap around the inner self to create paired different versions of all of the characters.
Yes, it goes overboard sometimes, but it also needs to do so as a means of camouflage as the inner story unwraps. We don't want preachy "look inside yourself" stories, but add weapons and violence and emotional buffering and battering, and you can slip the inner story under the threshold and make it something to consider.
As just a shoot'em up it is barely better than average, but with the inside story, the relationships in each of the two worlds, and how the two worlds are each real in different ways-- that really works.
It is not really a spoiler, but the final reconciliation is a nifty tear-jerker, and has a beautiful bit of bite that is amusing. In summary, the outer story is okay, the inner story is far, far better.