This one is cool. Maybe a tad brighter and shot from further back though just to make it easier to tell what it is. 2
It should be panned up a little more. Maybe if you had taken a step to the right it would be a little more even but I'd have to be there to know. Not sure if you're shooting RAW or what you're processing these with, but the blow out on the floor and the color fringing around it are a little harsh. Maybe shoot everything a little darker. I normally under expose everything by 1-2 stops and take a few different exposures for HDR, but mainly just to have options. It looks like the d3100 can do RAW so try it out if you're not. Just a warning, you'll need to export everything in jpg so if you don't normally process your photos then shoot and RAW and jpg if you have that option. 3
Again with the blown out highlights in the sun and color fringing around it. If it wasn't for the fringing I would probably say it's fine, but underexposing would give more room for editing as well as get rid of the fringing. Looks like it might not be level. The background also seems a bit out of focus so try closing down your aperture to fix that. I check every shot after I take it for focus and general composition just to be safe. I'm not sure what lens you're using but if you zoomed in a little and stepped back some then a little bit more depth could be added. Not sure if that's possible in this case or if that's the look you're going for but just an option. On the contrary, I wider lens and being closer could emphasize and dramatize the subject. I like the contrast in warm and cool colors. 4
I REALLY like this shot, probably my favorite out of them all. There's some really nice natural contrast and a smooth roll off on the light. If the camera was a bit lower and pointed up do it's level with the things I think it would be a bit better. That might not make sense but oh well. 5
This should've been super low to the ground and maybe a wider angle. Not sure if you have one but if not, an 18-55 would be cheap and cover a pretty good range. If you want it really wide then Rokinon makes sharp, quality built, and cheap wide lenses. A 10mm is about $350 USD new and a 12mm is about $250 USD new. And if this matter to you, they're made in Korea. They're mostly manual though so this might have a bit of learning involved. Nikon makes a 10-22 which goes for about $250 USD used. 6
It's just a pile of brush. There may have been an interesting angle or composition but I don't normally take shots like that at all. 7
Not sure if you meant to focus on the tree thing or the building. A shot of those stairs would've been cool btw. Like Steed said, that would be a cool spot for a model shoot. 8
This shot's really cool. It should be level though, and maybe if you panned a little to the right. 9
This one is also really cool. I'm assuming that the lighting conditions were less than optimal but black and white is a good way to fix that if needed. A few exposures would've fixed that, or just shooting raw.
Overall, nice set. You should probably invest in some more lenses. Don't bother with a new body though, even if the 3100 is getting old. Anything that has a reasonable resolution and manual control will work.
Hope this helps