Promising photos, it seems that you have some idea of composition and form already which is great. As far as the duck one, crop some of the top off..like 1/3 or so and that will bring the focus down onto the duck(swan? I dunno). As is the focus is on the lake because of the line that it makes which distracts the eye. Alot of the other photos are a little dark in my opinion. Are you using automatic or semi automatic settings? Because that would explain it perfectly, the camera will make the subject dark because it is adjusting for the sky. The skies look very good which is nice but the subject of the photos are dark. There are a couple ways to fix this but you'll learn better figuring it out yourself.
I like the composition of the bridge the best, though it would be nice if it had more detail. The urban shot is also good but again I would like to see it lighter because you are losing alot of detail and the people look a little too dark which is just annoying as a viewer. If your focus is on a particular face it would work if that one was lighter while the others were (just a tad) darker.
Hope this helps, let me know if anything doesn't make sense.
