Looks very unique and beatiful!

I can see the struggle between the gameplay comfort and the artistic aesthetics... so yeah, maybe thinner lines would be a good compromise. 
Although I think most of the dillemma is created in the first place because of the "small" size of the screen itself. It's really complicated to deal with split screens on a pixel-ly level of work.

Putting this aside, the graphics are really stunning! Very professional looking, colours are working nicely together to create unique ambiance for each background.
Also, the perspective effect gives a very immersive feeling.

I see. A thinner line, yes, I would definitely vote for that!

@Nami: the black lines separating the filtered/non-filtered art were suggestions from a friend. Initially there were no borders, but he said the art all blurred together and was uncomfortable to look at. From a gameplay perspective having the lines helps to better convey where the characters are safe onscreen - perhaps they should be slightly smaller from now on.

I made an alternate version of the collage without the lines so you can see the difference.

I really don't like that hars black line there :( Otherwise the art is great :)

wanna play it

looks great!