Whilst this painting is similar to another Van Eyck portrait, namely his Portrait of Jan de Leeuw, this one does have greater amount of details on the clothing which enables us to learn much more about the subject. For example, we can distinguish much more of this gentleman's clothing and from that we can then summise his approximate position in society. His outfit is fairly grand and he aggressively holds a stick, suggesting a role of power.
The stern look on his face is honestly delivered by Van Eyck who was an artist who liked to deliver reality as he saw it, rather than complement his subjects with unrealistic depictions. The model also appears to be wearing a wide rimmed hat but this is hard to make out against the equally moody background. Such a technique was regularly used to allow the subject's face to stand out particularly strongly.
The hands and arms in relation to the torso of the subject seem slightly unrealistic in form, perhaps this model was actually suffering from stunted growth. The hands seem to appear too closely to the body, meaning his arms were shorter than normal but this may simply have been a misintepretation due to the darkness that surrounds most of the painting.