My preorder came through a couple weeks ago, just in time.   I have an actual reason for this, as there is too much travel in my future, and too much time spent bored on planes or in hotel rooms.   Tomorrow being the prime example, as I go to Santa Fe to see Mom.   This entails feeding her breakfast and dinner and having little to do otherwise.

I've been playing with this thing for a couple weeks and my conclusion is: hot damn this thing is great.   Travel gaming options have never been great.   I used to use a PS Vita, but it made my manly-man giant hands cramp up if I used it too much.   The MacBook was better, but game options were limited and now it is old, crusty and has a broken screen.  The iPad in theory could have worked, but mobile gaming is a microtransaction ridden hellscape.

Steam Deck uses Proton to run Windows games under emulation, and it appears to work extremely well.   Most compatibility issues I've run into are about  the control scheme and screen size, not ability to run.   As examples, here's what I've played so far:

Rogue Legacy 2 (which I bought for the device):  Played for a few hours, long enough to beat the first boss, and explore the second area.  Perfect game for the device.  

Dark Souls 3: Other then their ongoing server failures, plays mostly perfectly.   I had to much with the controller definitions as it doesn't seem to recognize the R3 button for lockon.   On the other hand, the gyro-based aiming works well.  Not to brag, but I made it to the second boss (Vordt) without dying, so obviously the control scheme works.   I am not sure how far I'll take it as I've played this a ton on PS4.

Civilization VI: This was my test of non-controller games and...it almost entirely worked.   I played a complete game, and the device keeps up even during the end-game slog.  The track-pad mouse didn't take getting used to at all, really.   Only issue was that the screen is extremely cramped.

Fallout 3: I played through far enough to defuse the bomb at Megaton and clear out the nearby mall, so maybe four hours of gameplay.   Works basically perfectly (for a Bethesda game).   I.e. I did see some minor frame dropping.

Portal: Played for an hour or so.   Works perfectly.

Superhot: Mind Control Delete: Played for an hour or so.   Works perfectly.

Torchlight: Played for an hour or so.  Works...ok, but the control scheme is weird.   Fiddling may help.

I also proved to myself that Factorio runs fine, but I need to find a control scheme.

I also got a tiny travel keyboard, and hooked up a Bluetooth mouse.   Both worked trivially out of the box, so that's an option.   It also does HDMI out, so in theory I can hook this up to hotel TVs.

Battery life is decent.   I was able to get 3-4 hours playing Civ VI.

What shocks the me from 2005 is that a single long-hold of the power button and I'm in a fully functional Linux desktop.   I doubt I'll use it much, but could be handy.

In general, I'm very impressed at how the whole package is put together.   The controls feel great.   Even the on-screen keyboard isn't bad.   The entire device just feels nice.   (Though large...it's like twice the size of a switch.)   Though I've obviously spent lots of hours with it now on the couch and had no issues with that size.