It's certainly a candid, and if you like it, then it probably portrays something meaningful about your dad. That alone would make it a good portrait.
Now, as far as making it the best possible photo, you need to ask yourself whether certain things about it add or detract from the image, e.g., elements in the frame like the white patch on the right and the red cabinet door. If they somehow are necessary parts of the image to you, then you are set with regard to framing, even though portraits are more typically vertical. Further questions are the contrast and color saturation, both of which are quite high - do you want to dial these back some? There also is a slight yellow cast - I'm guessing this is incandescent light and average white balance - a color balance adjustment might be worthwhile. The motion blur doesn't bother me and may be part of what you like about the image as it probably captures the way he moves.