Hi AceCo55, thanks a lot for the feedback, very much appreciated! And thanks for the suggestion to post less photos, I'm sure it will help me get more feedback in the future!
I agree that 13, 15 and 16 do not have as much emotion as the others. I included them for the pineapple-like hair style in 13, the addiction to fashion in 15 (make up, nail paint, pearl earrings and BB smartphone on the arm) and the regal/noble look of an elderly athlete in 16. I agree that they are less interesting.
Completely agree with you on the softness. I would have picked a slightly different set for the worst photos from this point of view (for example 3, 4, 9, 10, 13), but there are indeed more than one that are pretty soft. At 100% size, it does not look like camera motion blur. I think the source of this is the AF (or the way I use it). Shooting close-ups, rather than full body photos, is pretty demanding on the AF:
1) Low depth of field, because of higher focal length and/or shorter distance
2) At the longer end, my 70-300 has a F/5.6 max aperture, which makes it harder for the AF
3) At the longer end, the elements inside the lens need to move more in order to focus
The AF system is the one and only weak point of the D90, which is an amazing camera, probably the best quality/price ratio available, but definitely not designed for action.
I hoped downsizing would make softness go away, but it was not the case. In the future, I'll try to:
1) Raise the ISO and stop down the lens to F/8 or F/9: unlike AF softness, noise DOES disappear when you downsize!
2) Leave the VR switched on, even if I was shooting at 1/800. Maybe a more stable frame helps the AF work faster?
3) Try 3D-tracking instead of fixed point (although I feel it helps a lot more for birds than for sports)
4) Get the D400 when (if?) it gets released!
On the contrast: again I agree. Yesterday I increased the contrast significantly (+20 on LR) and they looked good, but today I see them flat again.
Thanks again for your comments and precious advices!