The 337 is easy to fly (for a twin), has twin engine redundancy with
none of the VMC issues, displays good short field characteristics and
is available with turbo, pressurization and deice options. The main
problem is it is not a good trainer and instructors don't like them
(because they have no Vmc issues, they are considered "for lightweight
pilots"). The design is actually superior and the plane can take off on
one engine (although maybe not at gross and it's not in the POH and not
recommeded). True twin engine performance.

The fact that it was not successful says more about the anemic GA
market than the design of the plane.