Low contrast, edges too soft.
Also you have a low variety in shapes. Everything image has round forms, aside from the landscape you did.
I forgot to mention: you should get this book. It has useful and fun concept art briefs for you to practice with.
Really good work! If you want to work in that industry you're definitely going in the right direction, I recommend keeping up regular focused practice even if just a small sketch a day.
I found it helps me to think of it as a muscle you're trying to train, any art you do with the intent of improving is like an art workout that will improve your work as a whole even across mediums.
I recommend these books on getting into concept art and the industry if you're in need of direction :) Designing Creatures & Characters by Marc Taro Holmes for concept art practice, his prompts are good and gets you used to rendering ideas from other people (key part of being a concept artist) and Ultimate Concept Art Career Guide by 3dtotal Publishing which has a lot of useful information regarding the industry. (Also any books about art by James Gurney are absolutely brilliant tools for learning)
Marc Taro Holmes (an artist & art teacher I adore!) has a book on how to build a concept art portfolio. It may help... link on amazon