I think it doesn't look too shabby, but there are some things I'm not too sure about. You most likely need to work on your lighting. This includes the highlights and shadows on an object, where these highlights and shadows are, how big or long they are, and the like. The barbed wires look like their light source is coming somewhere near the top left corner, the grenade looks like the lighting is coming from the front of the image and also some spots from the top right, and the text looks like it's light source is coming down from a big light on the top right. This gets all jumbled up and is pretty much what can make an image like this look "pasted on". Fix up some of your lighting and also, add shadows where they should be needed. Like somewhere under the grenade. I, too, am not very fond of the text's shadow either, but I think I could see how it would look like without it. It'd probably blend too much into the background, so in this case, darken up the font. Also, I'd probably pick a different shade. And if you don't feel like removing the shadow, try adjusting the shadow to where it looks good, like maybe just make it look like a blurry stroke, y'know?
I'm not going to be much of a hardass on the black lines, but they could use some editing. Maybe mess around with different layer modes or try what JC said. As for the background, you should probably lessen the blur and maybe add like a gradient map or something to have a more realistic look. Additionally, don't blur the main object's floor, or ground, or whatever because it makes it look like the object is floating, and in this case, the grenade looks like it's floating ("pasted on"). So, that ground below the grenade shouldn't be blurred and only start the blur near the "back" part, if you get what I mean. Otherwise, good job.