I think you are right ... it does depend on expectations. I think SQ are good, but are they the unreachable best of the best - no. It all depends on several factors and an SQ flight can be awesome or just okay. Same as for other carriers
I do agree on the lack of a decent amenity kit, though note that SIA provides all most items you would usually get in the C toilets (e.g. toothbrush, shaver, lotions, etc.) and upon request (e.g. ear plugs). Call it eco friendly if you will
As far as the seat goes, again preferences differ. I know lots of people who love the SQ J seat. I don't dislike it per se, but find it a bit hard in sleep mode (back folded down) and not that comfy if you want to lounge (the newest version of the J seat is better with the lounging part). I usually ask for an extra blanket and put it on the seat to provide a little more padding in sleep mode. A little mattress would be great though.
YMMV.