Depends.
For the more casual player, a PS4 is probably enough for you, as it still gets significant releases now and then.
For the enthusiast, there are a number of really good games that are current gen only like say Stellar Blade, Split Fiction, Kunitsu-gami, etc.
Granted, I would say this gen is underwhelming so far in terms of the number of exclusives, due to economic factors extending the crossgen period way beyond the usual term, but there's still some good stuff that you just can't get on a PS4 or an Xbox One.
On the Nintendo side, it's still very early days for Switch 2, but I would say if you're a fan of say the Mario Kart or Donkey Kong series, then it's worth jumping in for those alone. Ordinarily I'd say if you want a broader range of titles then maybe wait a while, but these days you're probably better off buying now just cos the price will probably be raised at some point in the future.