How old are we talking? Final Fantasy VI, Super Metroid, Resident Evil 2, and the OG Tomb Raider series are all pretty old but great.
Portal, Portal 2, Mirror's Edge, Alien Isolation, Child of Light, Celeste, Tales of Berseria, Final Fantasy XIII, Slime Rancher, the newer Tomb Raifer games, and A Plague Tale are a few games from previous gens that hold up really well.
A more recent game that flew under a lot of people's radars is Kena: Bridge of Spirits, and it was a lot of fun. Also, Atelier Ryza and Alba: A Wildlife Adventure are very worth mentioning, too. :)
Kena: Bridge of Spirits really is an excellent game, I've done a couple of playthroughs at different difficulty levels, and there is so much more depth to the gameplay than I realized on my first playthrough. It's fun, challenging, has a decent story, beautiful environments, and some really cool bosses. The fact that it's an indie studio's first game still blows my mind.
Just wanted to add my own recommendation of Kena to anyone who might be interested, even though it's a more recent game.