Sony's PlayStation Now hasn't been of much use for nostalgia trips unless most of your memories revolve around the PS3, but that's about to change: the first wave of PS2 titles is available through the game streaming service. They're not must-have blockbusters, but they're definitely titles you'll recognize, including Ape Escape 2, Dark Cloud 2 and Hot Shots Tennis. And importantly, these aren't straight content dumps -- each of these games plays in HD (no 4K, alas) with trophy support.
This same batch also includes a handful of high-profile PS3 titles like Limbo and Metal Slug 3.
This doesn't include PS1 titles, and it's safe to presume that many of the PS2 favorites of your youth aren't here. It's a start, though, and it makes PS Now considerably more compelling. If you no longer have access to your PS2 or never owned one in the first place, this gives you a chance to revisit the games of yesteryear without hoping for a remaster or digging through your closet.