I learned early on, to test a mix in mono before the final master is made. If it sounds good in mono, it'll only improve in stereo..... that is, if you choose pleasing panning options.

Remember that dual mono approach the Beatles used? There are records that have only voice and drums on one side and guitars and bass on the other. Very distrete, and pretty weird sounding, unless you are in that one sweet spot that allows perfect bleding of the signals.
As much as I love the "Lads" ..... those early records had some anomolies that didn't impress me. Thankfully, the music always did !