Just my opinions:
#1: The very out of focus forground object at lower right distracts (esp since an in-focus shroom pops out of it with the stem leading the eye to it). I might have tried to crop it out - though that would have hurt the balance. B&W enhances the texture but I'm not sure the lighting improves it further. There is one "upside down" in the upper middle - there's always one in a crowd (I actually think that's the most interesting part of the shot! I would have focused on IT!).
#2: Very soft lighting. The in-focus subjects don't stand out well against that background. I might have tried a reflector to see if I could spot light the front set. Again, a lone out-of-focus one at bottom right a slightly distracting.
#3: Same as two with different subject. Here the in-focus shrooms dominate more with the focus running up to the top of the background set. This is better I think.
#4: Dramatic color and narrow DOF highlight this one. Though the background may be a bit overpowering for the subject, it is isolated enough to stand on its own. The out-of-focus foreground makes up a very small part of the image (which is good else it become distracting).
#4: Looks like a surface-to-air missile ready for armageddon. Subject is small compared to background making it look volnerable, but its intense chroma level balances. Narrow DOF - foreground is montonic and so does not distract even though it makes up a larger part of the image compared to #4.