As I know you have to buy games in PS Now. Not all games but top titles. Playkey also has many free games in a catalogue, even top titles.
I am talking about their unlimited subscription offering, which gives unlimited access to their entire library for a monthly fee of $20.
Also as of 2015, there are two ways to stream games in PlayStation Now, either as a subscription based service like Netflix, allowing unlimited access to all games covered by the subscription model, or users can rent games individually as can be done previously, usually available to rent in one of four time-frames: 4-hour, 7-day, 30-day, and 90-day. There are two pricing options in North America for the subscription service: $19.99 for one month, and $44.99 for three months.