Looking for some constructive criticism!

[twotonepunkkid]

I'm relatively new to the whole photography thing, and I've been doing quite a bit of video with the HDSLRs but no matter how many websites I plaster my photos on I can never seem to get very many good comments. I thought I'd try here. Please I encourage you to be as blunt and honest as possible! Bring it on!

http://www.flickr.com/photos/markklink/

 

[Kolor-Pikker]

Well, I've looked at the photos and there's some that I like, various nature and macro shots in particular, but there seem to be photos that could have benefited from better post processing, and some that I feel have too much PP.

What I didn't like were the portraits in particular, they definitely need some higher-end retouching... well, I wouldn't show portraits like that in any case.
The Niagara falls picture for example could do with less vignetting, or at least offset the vignette, since currently it causes too much interference with the subject.

Overall though, I feel like I'd have to step-by-step through the pictures to say what I consider good and bad, but you already seem to be doing better than most.