The artist is probably Daniel Gerhartz. (I have his book and it’s awesome.)
You need to keep in mind that he works with real oil paints, and digital is not very good at emulating most traditional painting mediums. You can do a reasonable approximation with the right kind of brushes, but you can’t expect it to look just like traditional oils–that’s unrealistic.
A big part of achieving expressive brushwork that can pass for an approximation of traditional oil painting, is to use appropriate brushes. You have to spend the time to search for and experiment with various custom brushes and match them to the different characteristics of traditional oil brushwork. For example, use speckled brushes of various densities to emulate the bristle marks of oil painting. Use various texture brushes to emulate dry-brushing. You won’t be able to emulate impasto very well, so don’t bother (even Corel Painter can only do a barely decent job at it in terms of realism).
You need to be able to reproduce all edge types–from sharp, firm, soft, to lost edges. right now, your edges are all quite soft, lacking definition and a sense of conviction.
When you study other people’s brushwork, don’t just look at the brushstrokes themselves and the textures of the brushstrokes. You need to analyze WHY the artist use that kind of brushstroke to depict that patch of value/color, and how that patch conveys a shape, or a texture, or a plane, or a turn of form. One of the key points of brushwork is how you choose to depict a sense of form/volume/mass with each brushstroke. Very often each brushstroke represents one distinct plane in the form, and each successive brushstroke represents a turn to a different plane.
You also need to actually watch master painters paint to see how they make their choices, because you will learn FAR more from watching the process than simply looking at the finished work. I highly recommend you get Richard Schmid’s painting demonstration DVD’s–they are the very best I’ve ever seen, even among the top painters alive today (and I have shelves full of books and DVD’s from various artists). He’s widely considered the most accomplished and skilled painter alive today. His captain’s portrait DVD is mind-blowing and will teach you SO much that you’ll likely end up buying all his other DVD’s (I own every single book and DVD from him, and they are all amazing).
BTW, in my workshop (linked in my signature), we spend an entire week on brushwork and line quality, and the assignments really push you out of your comfort zone and experiment with all kinds of different brushwork.
