1. The first thing my eye goes to is the dirt on his hand...second is that her hand goes into his in a way that makes her pointing finger look like a sausage. third the vignetting is too hard.
2. I think there should have been some kind of lighting on the ring to make the rocks sparkle...they seem a bit dull and doesn't really stick out in the picture.
3. I like the idea, but it's a bit over done...the fake flare doesn't add anything...it kinda drowns out the ring, when in my opinion I think the ring should be the focal point of the shot.
4. I think they should have been the the far left of the shot, maybe get her feet into the picture... and placing her right arm differently may have made for a more flattering pose.
5. out of focus BW shot + crumpled paper texture = not a good picture.
Overall, I think you've got the right ideas... and I have a hunch that the un-processed version of couple of them are actually better than what we see here. I'm no pro, not even close. My opinion is more of your everyday person looking at the photos. I learn more about right/wrong from reading people critiques on this site than anywhere else.