Quality obviously.
I remember reading from someone who worked at Gamestop a few years ago. A game like Wind Wake is $40 10 years after release is because people want to buy copies of that game but there is no supply. So stores like Gamestop would jack up the price to get a higher profit and people would PAY for it. Most people will buy a Nintendo game and never sell it because they love that game too much. This causes prices to never fall down because the supply of used copies never surpass demand. That's why Pokemon Heart Gold is worth more now than it was when it came out.
As for new games Nintendo never drops the price. They believe it creates bad habits for consumers and most of the time these games still sell well at full price. I mean I remember seeing a full priced Mario Kart DS at Gamestop back in 2012. Absolutely ridiculous.