It's a bit early to be able to answer such questions conclusively or with any certainty. I've had my camera since last Saturday and played around with it a bit over the weekend. I can confirm the positive facts such as better resolution with more FPS, significantly faster response time and compatibility with Hero 9 accessories. I didn't notice any overheating in the few hours my camera was running. However, this is certainly also due to the fact that the camera is sufficiently cooled on the motorbike thanks to the airstream and the associated sufficient fresh air. However, overheating is not just a problem for GoPro and can affect any camera in certain situations. I speak from experience. What I want to say... it depends very much on the intended use. All in all, I am very satisfied with the camera so far and would buy it again, especially at the current special offer price.

My device runs for about 20 minutes at a time at 4K 4:3 60 FPS before it switches itself off due to the heat. Outside in wind and weather, I can record about 2x 20 min videos before the battery dies. On average, the battery is reduced by 11% per 5 minutes, which is really weak. On Sunday I was outside and went for a ride. I took my Hero8 with me instead of my Hero 10.... That says it all what I think of the new device. I have no experience with the H9. However, the problem with overheating when shooting 4K is not unique to GoPro. Sony's RX100 or Canon's G7X are just as weak and sometimes only allow recordings for up to 10 minutes.

I have the Hero 9 + Mod and now also the Hero 10 + Mod. The Hero 9 manages 1h30m recording time at 4k/30fps/superview in the mod on my desk (without cooling/wind) before it switches off due to overheating, while the Hero 10 managed 58 minutes in my test under exactly the same conditions. The cameras are so hot at the time of shutdown that you can hardly touch them (at least on the bottom). Unfortunately, the cameras no longer run without a battery, only with a USB power bank (as was the case with the Hero 7, for example). So removing the battery for more cooling space doesn't work either.
The Hero 10 also had an error message once about the memory card not being fast enough (I have a SanDisk Extreme in it, so...), but that was only once. All in all, I probably wouldn't order it again and stick with the Hero 9 instead, but I won't send the Hero 10 back either.