The biggest hindrance to Sony's PlayStation Now streaming service is lag. Because the game isn't stored locally, whatever device you're playing on has to send your button mashing back to Sony's servers to process the input and then feed it back to your TV screen. That's changing. PlayStation 4 and PlayStation 2 games remastered for PS4 on the service will be downloadable as well as streamable starting today, according to the PlayStation Blog.
Source: PlayStation Blog