I've finally figured out what makes drawings appealing: shape design. I had heard that term thrown around a lot by pro artists and youtube tutorials (particularly Sinix) but never fully understood its application. After watching several lectures with a teacher thoroughly explaining all the parts there are to SHAPE and DESIGN I've been able to fix problems in my art I didn't know how to fix before.

Is the pose stiff? Add perspective, contraposto, etc
Are the colors dull? Check values, then shape dynamics
How to improve the shapes? Add flow and rythm to the shapes, overlapping, avoid symmetrical or repetitive lines, etc etc etc

With that said, shape design is not a fundamental, it only improves upon the foundation you've laid out.