A painted portrait of a person captures something that most photographs are unable to attain. Maybe it's the implied details, or the colors that the artist chose, maybe it is the small imperfections in the piece. Whatever it is, portraits have always been popular and timeless. It's also fun to exaggerate those portraits into caricatures.
Landscape paintings from life and the imagination are always a challenge. Environments, for an artist, are a true test of compositional, color, and value skills. It's easier to create a narrative with a creature or a character, but when done right; an environment has a story to tell and can captivate an audiences attention.
From concept to final, creature illustrations are a true test of anatomy skills. It's one thing to draw a person from life, but to bring an imaginary creature to life requires a true understanding of anatomical structures. Bringing a creature to life is a joy to do, and people love to see the imaginary come to life.
Every artist has probably been inspired by a cartoon. Simplifying and exaggerating the human form, objects, and places is a fun challenge to take on. Cartoons are a test of line, color, and shape language skills. As simple as they are, cartoons hold a nostalgic place in people's hearts and stick with them for the rest of their lives.
Sketchbooks are where an artist can explore, concept, and innovate new ideas. The sketchbook is absolutely the most useful and important tool to an artist. Miles and miles of paper are where the artist grows and achieves new goals in their technical abilities. Sketchbooks are also an unfiltered view in the mind of that artist and where the viewer can get a good sense of their style.