I recently got my hands on Horizon Forbidden West on Steam and I must say, it's surprisingly quite enjoyable on the Steam Deck.
I know there were concerns about it running on the Steam Deck, but I found settings that make it quite enjoyable. In one of the town areas, I was getting around 30 to 40 frames per second, which isn't too shabby.
I did have to fiddle with the settings a bit, but I found that running it at 800p full screen with FSR 2.2 on balance mode provided the best overall experience. You can try quality mode, but balance mode seems to work better.
On the graphic side, I set the preset to low, dropped the sharpening down to two, and upped the texture quality to high. With lower texture quality, the waypoint icons for fires looked hideous. I turned off the motion blur, and with these settings, I was getting around 30 to 40 frames per second in pretty much all scenarios, with occasional dips under 30. The loading spikes were also minor and didn't affect the overall gameplay experience. The FSR 2 upscaling kept things very tight and easy on the Steam Deck, and it was very responsive.
However, there was a bit of ghosting here and there, but it was more than playable. It's worth noting that the game uses around 22 to 23 watts on the Steam Deck OLED, meaning you'll only get around 2 to 2.5 hours of gameplay depending on the environment. On the LCD, it pushes it to the max at 26 to 27 watts, which translates to around an hour's worth of gameplay.
So, you'll want to be near a power source if you plan on playing for longer periods.
One thing that seemed a bit odd was that the achievements kept popping up, but they weren't registering on Steam. I'm not sure if it's a Decky plugin issue or something else, but it doesn't seem to affect the gameplay experience.
Overall, I found Horizon Forbidden West to be enjoyable on the Steam Deck, and I think I'll be playing it more in the future. It's more fun than the previous game, in my opinion.