I'm not an engineer, but conceptually the idea of a rotary engine still makes huge sense to me. Just looking at the number of parts in a Renesis vs a 6-cylinder reciprocating engine instantly brings to mind the silliness of the piston design, perfected, as it has been, over a century of R&D. Rube Goldberg cartoons come to mind.

Advantages in size and weight aside, just think of the cost savings possible in parts and manufacture were Wankels popped out by the tens of thousands. And yet, seemingly no engineering seems to have overcome the inherent problems of the Wankel design. It's becoming a moot point anyway, with electric cars slowly replacing the internal combustion engine.

Still, looking at that cartoon, it's hard to believe the Wankel isn't a better way to power automobiles.

 

The mechanics are simple, the thermodynamics are not
Thermodynamically, your regular piston engine is the simplest thing in the world: fuel/air goes into a static chamber, burns, heat pushes the piston. In a Wankel, fuel/air goes into a washing machine and has to somehow be burned uniformly and quickly in an irregular chamber that's moving.