In regards to the controls, there's actually a ton of buttons on the Steam Deck. You have all your standard Xbox controls and then 4 additional back paddle buttons and trackpad.
That's why it excites me: because I use a pretty weird control scheme, where the 2 attack buttons are mapped to the shoulder buttons, like in Dark Souls.
With those back paddles I could map them in such a way that my thumb never has to be taken off the right camera stick, which I tend to love using, especially during boss fights.
I still have a lot of questions, though, like I wonder if I can add PSU as a non-Steam game and have the Steam Overlay while playing.
If so, it would mean I could assign keyboard hotkeys to each trackpad. So when I rest my thumb on a pad it will bring up a mini UI with a bunch of keyboard shortcuts (you can map up to 16 shortcuts per trackpad) and you activate them by clicking in the pad.
It's kinda hard to explain, but basically it makes playing MMOs like WoW, which have tons of hotkeys, very playable on a Steam Controller / Steam Deck.