Thanks, all! I'm learning much from these remarks. Here's my afterthoughts/responses:
BoO was one game i never had, and never taken the time to play through, but i just watched a playthrough and do like what the title screen/ending does, among other things. Also for an '88 game, i think it looks really fine. Besides the comparison above, the columns i included may suggest something like that too. I am surprised noone has made a comparison to dracula's curse / castle of cagliostro theme yet!

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link to comparison of the two). I wanted it to be a reference to games and film taking place in a vague concept of Europe, rather than a specific location in the same. The column capitals in my screen are a derivate of the yonic style but made assymetric to denote something otherworldly. I think the ones in BoO are supposed to be doric or maybe toscan, but it's hard to tell and who knows what efforts they made.
I never thought of it as an underwater scene, but i can totally see how it can be interpreted as such. the blue field is supposed to be a misty lake with mountains and a waterfall in the distance, while the foreground is supposed to be cliffs above. The picture is supposed to convey two cycles of decline: first the temple site was abandoned, and then the adjecting, newer hamlet.
Regarding the mountains, i have a pretty simple rule set up for my self: the more distant something is, the less detail and colour should be used.
So, here's what i've gathered so far:
-Some tiles need to be less vaguely implemented, or edited to clarify the context. More specifically, the 'rotten wood' pattern i made for doors and which i reuse in the lower left for abstract background may be interpreted as seaweed or something. The lake itself may need some further definition to not look like a band of mist.
-The hithermost cliffside to the lake needs to be more clear?
-maybe lower the 'foreground' a bit
-make it ntsc-proof
-make clear rules on what is being used to convey solid and nonsolid. Even if this screen isn't meant to be playable, its assets would be used in actual levels.
-palettes can be reduced more than i thought to convey something similar, and the freed up palettes may be used in better ways.
I managed to add purple at the cost of a few extra tiles w/o palette reduction before reading these comments. I'll update when i have something more solid to show.
