Firstly, for better critique, stick to one or two images per post. It's too convoluted to really get in-depth when there are so many images.
#1 & #2. I think that the horizontal composition works much better here. Your subject is the bridge and it's a long horizontal object, so it just works better in landscape orientation. The bridge is quite dark, and if that was on purpose, then you would probably be trying to use the shape of it as the 'subject' of your photo. It does have an interesting shape, with all the structural members...but I don't think that you perspective really takes full advantage of that. If you wanted to emphasize the texture of the bridge, then you would have had to expose for that. But the bigger problem in these shots, is the poor light. It does look to be near dusk, but the overcast sky gives a very flat light...and also looks bland in the photo. The bland light makes the landscape look bland...so when we put it all together, most of the image is bland sky and bland land, with a very dark bridge in the middle. The sky does have a bit of color near the horizon...but I don't think that it's enough to save the image.
Suggestions for improvement: Choose your subject and what you want to say about it...then expose for it and adjust your composition for it....and since you are working with natural light, shoot when that light is good...not when it's bad. The most interesting subjects can look bad when in terrible light...and the most boring of things can look interesting in great light.
#3. As mentioned, it's tilted. When water is on the horizon, you usually (always) want to level that horizon. It just looks unnatural when it looks like the ocean should be spilling out the side of your photo. I do agree that a crop would make it look better, but rather than crop the sky, I'd crop from the bottom. The most interesting parts of this image (to me) are the silhouetted branches and the clouds in the sky. So by cropping off the bottom, it would focal the viewer's attention on the best parts. I would like to see a bit more contrast between the sky and the clouds here though.
#4. Again, the horizon is tilted. If you have Photoshop, the easy way to fix this is to use the ruler (measure tool). Drag a line along the horizon, then go up to the menu and click on Image, then Rotate Canvas and choose arbitrary. The box will already be filled with the angle you need to rotate the image.
I'm not too excited by this one. It does have a somewhat interesting foreground, so maybe you could emphasize that by getting lower, or maybe including more of it in the frame. The foreground (especially the rocks) look underexposed. This does give more color to the sky, but hurts the fore & mid ground. This is a perfect case for a graduated filter, which would allow you to keep the sky from blowing out while exposing for the shadows on the land.
#5 & #6 are much, much better. In these shots you have a foreground, mid-ground and background. That allows the viewer to 'walk into the scene', so to speak.
#5 would have benefited from a grad filter as well, because you could have darkened the sky, really bringing out the drama in the clouds.
The red moss in #6 is fantastic and the diagonal line of the waterway leads the viewer past the rocks and out into the background. That's the type of thing that really makes a good landscape.
As for editing, I'd suggest trying to emulate what a grad filter can do. In other words, darken the sky and/or lighten the shadows in the foreground. Don't be afraid to boost the contrast and saturation when you think it will help. I don't think that a landscape photographer has to faithfully recreate the scene as they saw it....rather they are free to edit the photo in order to let the viewer see it how they want them to see it. You can help to guide the viewer's eye into a photo by darkening some parts and lightening others. (burning & dodging). This is a technique that has been used by photographers for a lot longer than any of us has been alive.