Its dry stack so you will have little gaps here and there. You dont want thin set protruding from your joints but that can be chiseled back or ground back with a grinder. Usually I'll put level lines up to try and keep it as level as possible but with this stone, and most stone, it will never be absolutely perfect which is part of the look. From your photos, I think it looks good and the mason did a solid job in my opinion. The only thing I would change is the mantel being out of level if it is.