One feature that doesn't get mentioned or appreciated enough is the perfect sleep capability. I have 2 young kids and busy work/family life so I struggle to dedicate gaming time. I might get 20min or I might get interrupted in 30s after I sit down. No problem! You hit the power button and it sleeps instantly, and whenever you have time next you seamlessly and perfectly pick up where you were. This removal of overhead for booting and loading the game makes a massive difference for people like myself.
Otherwise, its interface is great and gets out of the way. There is any number of awesome games available and I've found I've played games I might not have on pc anyway. And a lot of games have seamless cloud saves too - for example I'm playing witcher 3 now and I can play here and there during the day on steam deck and then if I have time for a bigger session I pick it up on pc.
Games I've enjoyed on it include outer wilds (CANNOT recommend that one enough!), steam world dig 2, Dex, into the breach, backbone, and a lot of others.
Edit / p.s.: for me it's size is a plus btw. With Kishi+phone, Nintendo ds and even Nintendo switch, my fingers tingle and wrists hurt after a while. The wider and more natural spacing / angle of the larger steam deck means I can play with no such ergonomic issues.