How many hours should a single player game today be to warrant a sixty dollar purchase?

[Wagram]

10-15 hours for most genres like shooters. Quality hours though.
30-50+ for RPGs.
The sad fact is that in my opinion there are very few games worth full price. I can name a bunch, but I can name 10x more that aren't. Quality needs to rise significantly, and that's one of the reasons I no longer purchase day one for a lot of devs.