what does the work in mechanical engineering upper division courses look like?

Answer 1

a whole lot of applied calculus in thermodynamics, fluid dynamics, properties of materials.
some fun kinematics in machine component design.
a lot of fun in senior design project.
then about 10% of boring stuff like economics, ethics and current issues in engineering.
basically most of it is taking what you imagine to be fun, over emphasize the math, and then take a break for some 'managerial' type stuff.
of course that's just my opinion.