I flew this about 6 weeks ago on SQ. The service is amazing and the seat is huge. I'm 6'1" and had no trouble at all. The advice to get a bulkhead seat is good advice though, I did that it has a bit more foot space when the bad is fully flat.
I flew UA on the BKK-NRT-SFO route two years ago and there's just no comparison. SQ is miles and miles and miles ahead.