mmm. I don't quite understand if the "veteran" is falling or floating... of if he is at the wall, ceiling or floor ;_(
You could add some text explaining your intention with this minidiorama. So everyone could understand it better. But this is just my point of view so take it with a grain of salt ^^
On the paintwork.. I feel it is still missing some more work on the veteran. Yeah it's black but it is almost flat black (at least it looks like so in the picture)... If it's a veteran you could put some weathering on the armour. I like the eyes though.
Another problem I see is that the arm of the tyranid is the same colour of the background so it almost disappears... I am just trying to help here, because I like your idea and storytelling but want to push it a step further ;)