Right, we'll firstly, Welcome to
City 17 Pixelation, it' safer here. (Sorry, your portraits reminded me of HL2 for some reason
)
Anyway! on to the art! Your portraits have a a great style to them, very dark. unfortunately there shaped more like potatoes then human heads! so i think a rework on that front may be needed. (nothing to drastic)
Your also using far to many colours per head, especially on the skin tones, try working with a minimal 4 colour grayscale palette just for the shading and adding colour later, that'll give you a good feel for concise and intelligent colour usage.
Lastly, your heads are a tad guilty of pillow shading, look at adding a sharper and more direct light source. Overall though, certainly not a bad effort for a first post!
Nice to have you here Andy!