I’d always say get the exclusives for each system which means buying each hardware platform for each console generation. Not prohibitive if you time it right and get access to a decent back catalogue, which is pretty much where we are now. Still doesn’t help finding space under the TV.
First thing is PS+ worth 40 quid a year, but look for prepay codes or deals from cdkeys to keep the cost down. MonthlyFree games are a mixed bag of utter junk and a few decent ones to keep it worthwhile. Need to download monthly as you’ve no access to Past games. Anyway, onto what’s good:
God of war. Bad dad sim with blood and gore. Boy!
Nier Automata. Give it 10-15 hours or so, get into new game+ and revel in it. Future classic, join the cult now.
Not played Shadow of the colossus twice already? Play it, feel bad, you monster.
Gran Turismo up to the limits of a pad. I always found you hit a point at which the cars are too twitchy and powerful for a pad.
Last of us and uncharted combos.
Fancy a challenge? Not strictly PS4 only, but anything from From Software: Dark souls / demon souls series or bloodborne. Great games, but not exactly forgiving.