Ecco is probably the first game that gave me nightmares, I was scared of it but I also loved the aesthetic and the gameplay a lot. I wasn't old enough to understand from good to bad game design, not saying this game has bad design but most people would refer to it as insanely hard and mazey.
The third level if I recall correctly in the lower right side, that alien with multiple arms gave me the fritz and nightmares mixed in with the death sound of ecco just bwah... As I got older, I still find myself playing this game over and over. I didn't own the first ecco game when I was young but I had the second one. Which I have a lot more nostalgia for. Which to say it has amazing music and a good stereo play in there that makes it feel awesome. The first game is even more mazey and has creepy music and an even creepier boss with a red hue when hurt. Back to the second game, The backgrounds are amazing, the 3D-esque traveling is hard but feels great, the sea always feels lived in. The nature of this game is unique and there's not a whole lot of games that mix cutesy with aliens and a creep factor. Definitely worth a play.