Its a little fuzzy and the texture seems kind of 'thwacked' on there. It looks better smaller than it does full screen. But its clear what is happening.
Like cedricgo said, the values could use some work. Look up stuff for; 'value grouping', 'notan', thumbnailing'. You could do a lot worse than muddycolors.com to learn from several lifetimes of illustrators spilling their thoughts and knowledge. Just try searching those terms there..
If we are going to view it at this size, its hard to see the textures you included like the bricks and stuff. Make sure when you post your work to try to present it in the way you want it to be viewed. Not a lot of people think about this when they start out. If you want it to be viewed full screen tell people to open it in a new tab because most will view it at the forum size, and think nothing of it. You want them to stand in front of your painting or sit on the benches 20 feet away?
If you are going to paint and illustrate I would look up some more classical painters, or painterly inspirations both modern and historical. You'd be surprised how much they don't paint and how they allow the viewers brain to fill in the detail. 'Some' chain-mail texture is probably all we need.
It's more about feeling than being "right". I've been telling people that a lot lately.
Paint like you want your viewers to hear, smell and feel the painting. The way some writers write. When the viewers brain has to fill those things in people develop emotions for paintings because it "puts them there".
The 'why' is a loaded question, and you are going to get subjective answers based on who see's your post.
The "how" is what takes so much time to explain in non video format. Look for tuorials from your favorite painters and try to replicate their techniques. You will find that you either enjoy or dislike their process even if they have end products you enjoy. Learn how to control, then how to express. Masters don't teach pupils how to combo strike opponents starting out, they teach them how to stand.
