Hi Milan,
Thanks very much for the detailed reply and checking out my portfolio.
You’re right. The space ship crash shot was definitely my hardest challenge to date.
For challenges of trees, landscapes, or modern building there is always additional reference hunting that can be done if I can’t find the right look.
The crashed space ship was a lot of guess work … the initial 3D pass I was given was very low-poly and pre-vis level… although it did give me my initial lighting and proportions (which was helpful)
I painted over most of it completely and by then the composition had changed significantly. The 3D for the shot was re-done after I completed the 2D matte painting… so it didn’t really become an environment shot until the end.
I used reference from the set itself for the foreground rocks, waterfall reference for most of the chasm… the deepest area was painted and pieced together by using earlier shots from the movie.
I had to figure out what many of the props and set would look like from an aerial point of view rather than eye level.
It was primarily a 2D painting however. It is also a little hard to believe that my hardest matte painting to date was a lock-off and not any of my projected shots.
I’m extremely impressed with your fully cg shots!
I’ve worked on some smaller cg shots, but nothing as epic as the New York paintings you posted.
You should be really proud 
Thanks again for answering my question with images.