player will not even notice there are shadows at all if the gameplay is good

I think game grafix need to be smooth and consistent.
It is not so important how high the resolution of texture is, or if a building is blocky.
But It should not stick out of the rest of the scene!
Same with the Treeshadows, if everything casts shadows,
it would stick out if they are missing an trees. But If they are there, and not fully correct, the player will
not notice while concentrating on the gameplay.
For me the grafical part is not the main element.
It only serves to create a certain athmosphere, together with the sound, music, story
and gameplay.

Even If you have an ugly Artwork: if this is consistantly ugly, it wont harras the player
as he gets used to it, and concentrate on the gameplay.

Same with shaders,
I dont want to use them unless really required (like the terrainshader, that I need).
After a while the shader will not add much to the gameplay,
but it will reduce it a lot : lowering the Framerate.
Now some people here implement shaders at any cost, if the framerate drop they either
state hilarious minnimum requirements for the game,
or reduce the content in the gameworld (models, Blocks) to increase the framerate it.
Why not kick out the shader in this case?

Consistant crap (like in a horse-barn) looks less disturbing than
a pit of crap on the front of your new Mercedes.

True, thats ok for certain effect shaders.
They are a nice optional addition.

I am talking more about shaders that dominate a certain scene.
Take the bloom for example. When using bloom, you need to change
the brigness and lightning of the textures in your game to make it all fit together.
Now if the player switches off the bloom, it will look really ugly and inconsistant,
as the scene is too dark and has a strange contrast.
So I would have to eveluate, what brings the bloom to enhance the athmosphere, at what costs (FPS).

Other is the usage of dynamic shadow casting shaders.
They are used even if the gameplay does not require a dynamcical shadow world
in the end. And they really drain performance. (thief 3 as a bad example)
Now if the player needs to turn it off, the game will look really ugly, as
the whole shadow part is gone, that gave the scene the needed contrast.

Absolutely. I agree with you. Dynamic shadows are not always needed.

Concerning the Bloom / contrast problem: Maybe it could be solved with lighting. When you switch on the bloom then you could darken the whole scene via sun light properties and so it could be a cheap solution, not artistically perfect but it could work.

Modern games mostly have the ability to switch on Bloom or HDR. So it can be solved.

Here the trees with a shadow
I ignodes the "leaves", or
it would generate strange dark polygonshadows.

I just noticed another big bug in my renderer.
That places the shadows in a wrong angle on higher terrain ...
If I ignore it, the terrain gets selfshadowing, that looks
not the way I want it. (the terrainresolution is too small for this
to work good)

That looks great. Ignoring the leaves is no problem.

Yeah, I second that. I only noticed because you said so.

Cheers