I'm a videophile and have been using Avisynth (Vapoursynth mostly these days) since the DivX vs Xvid wars and every year I give x265 another chance only to be disappointed. There's also the hardware compatibility issue but regardless the quality would still have to be there.
Take a look at the most popular outstanding bugs and you'll notice many of them are regarding quality [1] The doom9 forums is also a good source. Many have posted comparisons proving the point.
[1] https://bitbucket.org/multicoreware/x265/issues?status=new&s...