Actually, I think you've been improving a lot your skills lately, picture by picture...You have already a personal style and taste for colors and I'm pretty sure you already know which are your Achilles heels. My suggestion is if you want to keep portraying and do character design, keep up the good works. If you want to be "complete" because your goal is to be a concept artist, so try different stuff (as I read, you're working on a GOW picture), more architecture, mecha and tech stuff could be a nice input. You can also try to experiment dynamic poses, or different light sources, you can challenge yourself with a picture that describes a scene and not only a character maybe, or an atmosphere...as you can see the way is almost infinite, but so damn funny!
I'm sure you'll reach all your goals!

Everything is amazing! (yes i know it's not very helpful) maybe you could do backgrounds more, because you usually do portraits (which I love)

Your are a great artist - loved your art first time I saw it - however you keep painting the same thing and it is getting a little bit boring. Would love to see something different from you - you got so much talent!

Oh, good lord!
I have like, fallen blindly in love with your art, and I don't find myself on a level where I can share any knowledge with you (I think it should be the other way around.)

But I do agree with the previous people who wanted you to draw some men That could be pretty interesting!
Maybe you could do some more full bodies and a few more elaborate backgrounds and perspective? I found only one that had a full background so far...