For me the big thing with QF F is the seat/bed. Specially in bed mode. On a 12+ hour long hail, for me, the difference is real (I find the J suite to be a tad narrow for me). The food is more or less on par with J with just one or two other bits and pieces and the French bubbles but the big one for me is the relative privacy and the space and comfort of the bed product.
Even tho9ugh it's 15ish years old design wise, it's still very good at what it is very good at. Other aspects not the best compared to some others.
As Matt says.. Service is another conversation. Had some magnificent F crews.. some who have remembered me from other flights (which is a nice touch). and I mean REALLY remembered, not just "welcome back Mr P1" and had a personal touch. Others have been a bit... hmmm well.. "unique" and even the odd one who made me feel like a simple request was a real chore.. but we all have days like that and I don't judge the whole product or staff based on one or two.
If I had the choice between say SQ and QF then it's a no brainer but for what it is, and keeping expectations in check, it's far from the worse "F" product out there (even with the various jokes about mini First and all that).
And, the value proposition will vary depending on how one gets into the cabin too. eg no way would I pay for QF F with $$$. points sure. Upgrade.. sure... potentially a decent (ha!) sale potentially. eg some years back there was one of those "buy J, have F one way" type deals to LHR. It wound up being about $1k or so difference cmpared to a cheaper J sale at the time for that one way F sector. For me that was a no brainer value wise. Plus I was upgraded on the J sectors anyway but ti was nice to have the confirmed F already booked in and for me that was value. For others maybe not. Again, these things are very much subjective.
Each o their own of course.