[Buschel]

First honest impression: OMG. This is really for the worse. Please roll (most of) these changes back immediately.

I cannot roll back anything. As I wrote, nothing of this has been even merged, it was just a build to gather feedback. If I cannot do this in TF, I cannot do such kind of changes anywhere as no-one else seems to work on this app, builds on his own and shares feedback this way.

It doesn’t look centered, at least it is misaligned with the app’s navigation bar on the left. I know that these are independent UI elements and don’t belong together, but it looks bad IMHO.

On iPad it is as centered as it always has been. I need to work on iPad which is not properly handled since I took over the maintancence. On iPhone it looks like this:
https://ibb.co/Lnyg5Bc (new)
https://ibb.co/n7MXvGD (before)

showing some of the issues with the new layout: misalignment, most important information in the smallest font possible. Why?

What you mean by smallest font for most important information? Only the font for the time has changed, it was increased. All other fonts are same size. Screenshots for iPad:
https://ibb.co/vqyXYZz (new)
https://ibb.co/rsnj9MJ (before)

While I like the emphasized Play/Pause button, I don’t see any reason to invert its colors, because now it looks somehow like a "selected" button.

I like especially this highlighting. This looks very similar to Spotify's design.

Good. But the overall layout now is somehow squeezed, not making use of the wide screen any longer. Movie and song titles are truncated and shown in a much smaller font than less important secondary information. This is a also huge step back.

Can you please show examples of squeezed or truncated song names. Don't you feel that the wide progress bar was a bit too much? I am not using an iPad but always felt that the need to touch that far left or far right to move the progress bar was a usability problem.
What I now recognize is that files which do not have proper meta data (like in your screenshot which only shows a file name) look not good with the new layout. Old layout had this one name listed right under the progress bar which kept them visible aligned. The new layout only looks good, if all text fields are filled. Need to think over this.
But again, motivation was to move the slider down for easier reach when using one-handed.

iPad: clear playlist background to show the underlying fanart

Don’t see this?! What do you mean exactly?

Just add one single item into the playlist, play it and the extend the playlist size up. You will see there is no gray background anymore, but just the fullscreen fanart background.

And the overlay icons are now too low, almost glued to the bottom of the artwork, making this looking bad either… Not talking about the HighRes Audio icon now completely lost in the upper left corner of the overlay?!

What's the problem with the icons at the bottom of the overlay? The HiRes icon I agree, but I needed to place it somewhere for now.

If a specifc season is unfolded, it will be closed after selecting any of the newly introduced features. Very annoying.

Yes, I am aware. Difficult to resolve without overdoing the whole implementation. Let's see, if I can rework this.

For some strange reason, I observed the following side effect on the Kodi Server screen (i.e. not in the app): The screen starts flickering while the individual episodes are touched by the app. Also very annoying.

Great. This is what you get from adding a feature which the API does not support. Maybe I should stop this and wait for the API to support it. What a waste of time.

I know that it must be frustrating to receive negative feedback after you put so much love and effort into the redesign.

It is, but it is important to receive such feedback to not move into a direction which is not accepted by users. But this is what TF builds are for -- testing.