So, we're only supposed to share impressions of our own games, but I think no one will complain when I say that I've played both Death's Door and the Lodoss War Deedlit game for several hours each without any issues and great performance.
Now for more in-depth impressions on our own stuff: so far I've only tried ToCS4, but it runs really well.
There is an initial shader compilation frametime instability, but from what I understand this will be taken care of for the release version by distributing shader/pipeline caches via Steam. After that initial issue and once the pipelines are cached, it works perfectly. 60 FPS at native resolution with PS4-equivalent settings, and fast load and map transition times too.
Regarding the system overall, here are some of my thoughts.
Hardware
It feels really good, and very ergonomic to hold. All the controls are easy to reach.
The shoulder and back buttons both feel much better than their Steam controller equivalents.
The D-pad felt a bit mushy at first (at least for my preferences, I prefer it more clicky), but in actual use in a demanding (in terms of input) 2D game it works really well. And when I tried it again just now I can't even really understand where my initial impressions came from.
The one thing that's actually problematic in this prototype (or more specifically my unit) is the "B" face button. It's not a problem to reach or press it (which some might think due to its placement on the very edge), but it can get stuck/wedged in somehow ocassionally. I think the initial journalist impressions already mentioned this, and I assume it's resolved in final HW
The screen gets really bright. I had to turn it down to 15% or so on the slider to comfortably play inside in the evening (note that I generally don't like high brightness screens).
Talking about the screen, it seems nice in terms of quality. I've noticed no ghosting, and contrast seems quite decent for LCD.
Software
The overall software feels great, very suitable for a handheld and easy to navigate. Having 2 distinct buttons for OS/non-game functions to bring up overlays related to the HW on the one hand and Steam on the other is very useful.
Proton works amazingly in all games I've tested.
However, this is very clearly still in pre-release form. Important features were only added in the first software update I did (e.g. just having an option to set a timezone in the UI), and I've also managed to hard-lock the entire thing once already.
One thing I was particularly interested in is suspend/resume since it's technically challenging to get that to work with a massive library of legacy games. So far, it worked perfectly in all but one game I tested. In that one game, audio was crackling after resume -- I think that's probably something that can be ironed out. Suspend currently takes around 2-3 seconds, resume 15-20 in my tests.
Can't say much about the battery life, except that it's very clearly highly dependent on the software you run. I'd say ToCS4 consumed roughly twice as much battery power per unit of time compared to Deedlit