These are pretty neat!
I'd love to see something free drawn from you, though. I guess that's just my curiosity kicking in. I'd say a lot of the characters have really neat fashion sense and design - I would just be careful with your shading techniques if you're trying to go for a Ken Sugimori style. I think most of your work look like Yusuke Ohmura though (I talked a little bit about his style in one of the spoiler tags below!) - but it's still looking like official Pokemon artwork.
I agree with Lornami on the comparison of your strongest and weakest works. The strongest pieces are blended well together and have some better brush strokes that aren't as harsh as the weaker pieces. I also can't tell if you meant the order was from oldest to recent or the other way around? I checked your DA gallery and it seems like yes the top is the oldest work. Anyway, I waned to talk about some of the recent pieces then!
For example

It's not bad, but the shading could have been tackled a little differently.
First; gotta expand the hue range

Wether you're going for Yusuke or Sugimori style: they have some variety of hues and values.
Comparing that to your first piece:

You get slightly different hues AND values.
So, I compared the hair value and hues to Ken and Yusuke so you can check out the difference (and you can see how they shade)
So you get an idea of their styles! I took one of your recent works and made some notes.
Pretty much what I'm saying in my pile of messy writing is:
- Try different hue ranges
- Try less harsh shading
- Leave subtle hints of light
- Play around not only with huse but with your value range!
BUT I GUESS EITHER STYLE YOU'RE GOING FOR: it's close to "official" looking artwork. ouo Just keep note of your values, different hues, and try maybe a softer brush when shading? I hope i was somewhat helpful!