|Hi Daniel, welcome to the Critique Zone!
Where to start? This is an interesting shot, lots of detail and I think that you have succeeded in achieving the DOF that you were after, so good job there!
Technically, this is not soft at all, I don't know what that comment was about. Focus is very good all the way through. For me, it is the lighting which is a slight problem. Because of the angle of the light, you lose the shadow between the 'layers' of the shell and on the right, they merge into one. It is a very harsh light too, perhaps with too much contrast between the very bright right side and the dark left.
Artistically, this definitely meets the challenge. It's a great subject. I think you would get a very interesting perspective by angling the shell slightly to point to one of the corners, fixing the lighting to drop shadows behind each 'ridge' to get a really deep composition. I also have to admit that I'm not crazy about the blue colouring - perhaps a good subject for black and white?
I hope that didn't sound too negative - it's a really nice shot. I am just trying to find some things which might be of interest to you to try for next time!