Thanks for the feedback. I will try to improve with your tips.

I really like it, but feeling we are not capturing how to make this piece even greater. First - regarding lighting source consistency (direction) - leave it, it looks ok. The composition is fine, looks eyecandy. The black outline - there is a huge contrast between the black the lightest colour that is the nearest to that black. In most cases you could replace the black with darkest rock colour (which is dark grey). If you want to go further - you could replace black for grass/trees - with darkest green which is the shadow's colour. At the end - you will see nice colour consistency. From other points - repeating patterns. Roof, trees, bushes - too much spontanous shapes, sometimes the shapes gets more oval, once more square. Not saying to repeat the same shape - but the same pattern. The same goes with symmetry, bushes/trees would look much more clean if the shape was more mirrored. When you are making lines try to go with pixels lengths like 1 2 3 3 2 1 1 2 2 3 etc. to make the curve line more smooth, going 1 2 1 2 makes it less sinusoid, sadly. At the end - this is a great piece, just feeling that cleaning up your ideas will make you 1 level above artist and the piece will be outstanding.

Keep up the good work! It's definitely a nice mockup. Eishiya made some good points which will work good for your next pixels! 

While drawing by hand will give the best results, if you do want to use an overlay, you can get better results by using a colour other than black. Your shadows seem to have a slight bluish or purlish hue to them, so if you use an overlay that's a dark purple, you'll get shadows that fit better with the rest of the art. Using a different blending mode can give better results too.

Another option, especially useful if this is meant for use in games, is to avoid long cast shadows in the first place, and have small shadows at the base of the object instead. This'll look flatter, but such shadows are quick to hand-draw, they avoid issues with shadows interacting with objects and characters, and you won't have to think as much about light direction. Long shadows are very useful as a composition tool, but you don't seem to be using them that way here anyway, so why make extra work for yourself ;D?

Looking back at this drawing i completely agree with you. It's true that I used a low opacity black layer for the shadow. I think you are right and I should draw them by hand like the rest of them. Also I should be consistent with the light direction. 

Thanks for taking the time to comment. I will try to apply your advice in my next drawings. I'm really grateful for your feedback.

I like the cartoony style here, but I think the shadows could use some more work. Their positioning is inconsistent, the cast shadows from the house and trees suggest lighting from the north, the shadows on the trees/bushes themselves and on the rocks suggest lighting from directly above, the shading on the house roof suggests lighting from the west, the hill the house is on appears to cast shadows both towards the east and west, but not in the same direction as the trees and house. The colours of the shadows also look like you just made a black layer over the piece at low opacity, instead of colouring the shadows with the same care you put into the shadows within the sprites and tiles.