I like the color tones and the light. It's a bit dark but I think it's fitting, and you can generally get away with some dark eyes in such a moody portrait. The face could use a tiny bit of dodging just to polish his skin tones, and perhaps a slight boost in brightness would improve this shot as well.
If you plan to do more portraits, I would recommend using a white reflective surface held below the portrait subject's face to reflect a tiny bit of light back into their eyes, especially in a back-lit shot like this. Doing so would add reflections and light into the eyes, giving them some life. You can pick up a 5 in 1 circular reflector on amazon for less than $20, but really any white surface that reflects light will do, such as a piece of white cardboard. Once I even had an assistant hold a white t-shirt in front of the model just for that reflection, and it works.
For not having much of an interest in portraits I honestly think you did quite well, and I'm very picky when it comes to portraits. I hope you do more.