Some points --
- The black and white levels in your scene does not match. Looks like its a kind of collage or cut out ...
- The composition of your scene is poor ( at least to me). If you can make a viewer lock on to a single object of importance that should help. Some things are distracting Like the birds at the extreme corners. The flowing water .. Maybe a pan might help ..
- The grading does not have a Z-depth cue hence it looks flat ..
-Lighting looks a little un natural .. I guess Light direction and shadow should be kept in mind.
these points are not to discourage but help your artwork to make it look outstanding ..
... cheers !!