Nice work. It looks pretty authentic at thumbnail size, which is always a good sign in painting. When I enlarge it I see a few things that you could do to make it look more "Rembrandty".
First is color temperature. Your blacks are cooling off a bit too much. Especially on skin, and especially for a Rembrandt, your darks are going to be very saturated. If you are using ivory black you are going to need to warm it up a lot to get the right tone. Ivory black is like a very dark, cool grey. Almost a blue. Keep that in mind.
Second is edges, and by that I mean the borders of your shapes. Rembrandt was a master of edges, and he loved soft and lost edge. Your edges are a little on the sharp side now, especially around places like the nostrils, eye, forehead. Those are round forms on the body, and so give them soft edges.
That might not be what you see, you might see hard edges. But remember that is because your eye instantly adjusts to where you are looking. For example, when you look in the shadow you see lots of detail, then when you look in the light your pupil opens up and you see lots of details again. This is an illusion that you have to adjust for.
If your focus is the eye, then paint the cheek (for example) the way it looks when you are looking at the eye. Try to look at the cheek with your peripheral vision, and paint THAT.
Think of hard edges the same way you think of pure white. The lightest highlight on your entire painting gets the white, and everything else will be darker. Similarly, only the sharpest edge in the whole painting should get the sharpest edge you can make. Everything else will be less sharp than that. In fact most edges will be quite soft. On Rembrandts lots of the face will actually be lost in a brown fog, which if you think about it makes no sense, but it looks fantastic.
So, using warmer tones for shadows, and trying to lose edge, I went over your painting a little in photoshop. My main goal here was to bring back the big, round forms of the head. Ignoring small details. You can see it's a little more Rembrandty:
If you're painting is dry now you could achieve this effect by using glazing, and as a bonus you'll get the lovely transparent effect as you build up the layers of paint. Start by glazing over the darkest parts of the face with a dark, transparent red thinned with linseed oil. Good luck!