Damaged or partially destroyed buildings always involve a lot more work than perfectly clean ones as you have to put in so much more detail in the rubble and damage - two things which you have plenty of here.
However, what lets the piece down (in my opinion) is the small palette, and lack of texture. The roof tlies are very bland, and the ground that the church sits on, althogh there is some scattered debris, is flat and just one shade. The cracks in the building look a little too regular in tone, whereas in reality light would catch them differently and produce darker crack lines and softer ones. Also, as this is meant to be an old ruin, what about some moss growing out of cracks or on the tops of the walls. I'd also have maybe prefered to see a part of the church missing more tiles and just showing the wooden struts.
Still, as I said, half demolished buildings are always very tough and this is definately one of the better ones I've seen - well done and keep it up!