Firstly, the lens produces crisp, saturated images. I haven't checked all the EXIFs for shutter speeds - as I have a VR lens myself I am aware of their awesome capacity.
The pix that work better in your gallery are the ones where the water-ski action occupies most of the frame. Pic #8 is a great action shot of the skier, but would have been much better with a more blurred background or different viewpoint to eliminate the cluttered background. #7 is better in this regard, but perhaps would have benefited by being able to see more of the tow-boat and having the skier in the upper one-third of the LHS. #5 may be improved if you crop out some of the white marquee and bystanders in the background.
Working in such a big arena as Darling Harbour is a challenge, even with a long telephoto, and the photographers vantage point becomes critical. Framing your image so that all of the action is not in the centre of the frame is difficult, but you must do this to have better than average work in this difficult field.
Don't be discouraged - you are presenting images and asking for honest feedback, so if you continue to do this and are prepared to listen to the criticism that makes sense to you, you will undoubtedly improve.
PS - I looked through the rest of your galleries, and you are obviously quite an experienced, and good, photographer. That's why I didn't waste your time complimenting you on excellent focussing and exposure - I figured you were looking for something a bit deeper. Hope I was right!
Trevor