the first shot, for being a run-of-the-mill eye shot, has pretty good composition. the eye isn't centered and staring at you like everyone else does when they do this. the focus is more on the top lashes than the pupil, but the lines of the lashes draw you down into the pupil. makes it more interesting. I can see what the people are talking about when they say it's obvious you edited it, though.
the second shot is kinda awesome ^_^ love the play of light. I do wish the rest of the bottle was in focus too, but it's not really necessary, I think. it works as-is.
the third shot is pretty mundane. it's a cat doing nothing interesting at all, and the composition isn't that interesting either (though, I know how hard it is to get a good composition on a live animal.)
the last one is spectacular in some respects, and kinda bad in others. the colors are fantastic - the oranges and reds versus the blues and greens. complimentary colors - it really pops, and draws your eyes in to the piece. the bad thing about it, is the lack of subject in your picture. once your eyes are drawn in, they wander all over the picture without really having a decent place to stop and take in what you're looking at. the bottom of the picture is very chaotic.
I'm kinda figuring you were going for a repetition shot with the trees and the lines of the rollercoaster track and support beams for it, but it's hard to even realize there's repetition in the picture right away. if you have access to get to this spot easily, I'd suggest you go back and try some different things to improve. try to eliminate the chaos. it may help to get more in the shot with less (use less of the rollercoaster to get your point across), and try to keep the
rule of thirds in mind. the picture is cut into halves, both horizontally and vertically, and it's not really working.
keep at it!