I appreciate your feedback and did some edits in the last days.
This is just the current step and it will of course not be the last one. There are still things to be improved.

All the following perspectives are from the viewer:
- The horizon's colour order has been changed back (dark -> bright instead of bright -> dark)
- Nature in the back got changed
- Pine tree got changed and is my greatest enemy at the moment
- The left shoulder has now the same length as the right one
- Her torso and neck are now more detailed
- The bag's holder has a new texture/lighting
- The right eye has been updated and is brighter
- White dots were added inside the eyes
- Her clothes' lighting got changed
- Small stuff
Well the pine tree is my biggest issue at the moment : / I have no clue what I could do with the surface on which the photo is taped on. A texture would be too distracting but I might change the shadows in the corners.
Additionally in my opinion I have to improve the grass, too.

New progress which is still not fully done. One idea is to make the very far of the ocean brighter but the nearby water dark. Additionally I will try to make the waves smaller and smaller the more far the distance moves.
The shoulder got redefined in terms of lighting to reduce the perception of a flat character. Therefore I tried adding more volume to the face, too. Still not very happy with that.
The pine tree might be reworked completely soon. Though I have no clue how handle it. Right now it is just a terrible mess of unreadable pixels in my opinion.
New attempt on the pine tree.
I tried to clean up the tree and correct the shapes.
The old one was too noisy and uncontrolled thus I could not bear looking at it anymore.

New updates!

The ocean got changed again.
Trying to make them becoming smaller nearby the horizon. Additionally the very far of the ocean is now a prettier.
The grass area has been adjusted.
Flower pattern are more consistent and feel more organized to me.
Some small edits on the grass area, too.
I added a few trees onto the hills in the very far. Alternatively I tried using a darker brown behind them to indicate some more pine trees but I did not like it that much.
Max's hair has been slightly changed. Some missing AA was added, too.
My last point is the front pine tree next to Max. I changed a few pixels on it.

First of all I tried to increase the shadow around the nose!
Additionally the background on which the photo is being taped on has been reworked.
Last but not least some highlights on the ocean has been added.
Still not sure what to do with the shades in each corner of the taped background, though.

I call this done.
The reasons are quite simple: This piece taught me enough and I do not feel any progress neither in the piece itself nor in my development.
Thanks everyone! I appreciate your help

I uploaded it to the pixeljoint gallery and deviantArt already:
http://www.pixeljoint.com/pixelart/94644.htmhttp://lakelezz.deviantart.com/art/Max-Caulfield-Life-Is-Strange-531640243