Honestly the lack of strong BC hurts, i was almost tempted to get a OneX just to play OG xbox and upscaled 360 titles these past few years, and when you consider how larger is the games-pool PS5 could dip into, it sucks they're considering as a bit of an after thought.
That said, PS1 and PS2 emulation is way ahead of OG xbox emulation, so at the end of the day, not that big of a deal.
As long as they support PS4's titles strongly, they should be fine on that front.
Also they focus a lot on 3d audio, which is cool and all, but personally i play 90% of the times with a regular soundbar+SW, so i'm gonna get shit out of it.
I assume most people play with headphones, though? I dunno it'll be good for them.