First things first: I'm a fan of the pen sketches you typically do, but I'm glad to see you trying something different. Stepping out of one's artistic "comfort zone" can be challenging and risky, but you took the plunge. Impact, for that reason, gets a 5. Vision gets a 5 too, because this isn't the kind of art we typically see from you, and it looks rather a lot like what it should: a ruined cathedral.
That being said, originality tallies in at only a four. This isn't the first or last (by far) post- apocalyptic cathedral on DA. If it had been, you'd get a 5. For you, this is original, so I'll give you a four. (it would have been a 3.5 or so, had this been not the first post apocalyptic cathedral you made)
Your technique here is pretty good. I know I couldn't (or wouldn't have the patience to) do that kind of stuff with photoshop or other photo editing software. My one gripe with it lay in the fact that what parts of the cathedral aren't completely ruined appear to be perfectly pristine. There should be some blending of the two. (bleedover, if you will. All those chairs just sitting happy as you please under an open sky/collapsed roof? not likely.)
The roof also looks a little too "cut," if that makes any sense. (not a single detail of the outside roof either, but that bit is beyond your control in the case of a photomanip, so you didn't lose points for that reason, just for the other.)