1. The first party, deck verified steam experience is super smooth, feeling just like a game console. It's like a switch with a deeper library and better controls. I love the community contributed control layouts as well.
2. The hardware itself is fantastic. The controls are great for both gaming and light desktop computing. Great feel in the hands, pleasant screen for gaming, and really just a much more comfortable experience than sitting at a desk or playing on the TV. It feels like curling up with a good book.
3. Linux with great windows compatibility layer out of the box. You pop it over into desktop mode and you have a Linux machine with ability to run most of the software out there for windows. You plug in a usb-c hub and you have a full desktop, keyboard mouse experience. And if you really have the need, you can dual boot into windows.
4. An insanely helpful community. Tons of knowledge out there for getting it to do anything you can dream of. So many people hacking on their favorite game to improve performance or play experience. Many folks writing auto-config scripts for anything from turning it into a retro gaming powerhouse to tweaking the swap file performance characteristics.