I have tried build 10572 on my Lumia 720. (My previous attempt was only at build 10166. After that no time to try)
Following are my observations:
1. After upgrading last Friday, my micro SD card was not detected and hence all the applications which were present in Micro SD were not working.
2. On Saturday, when I was trying various applications, my phone got frozen and I had to soft reset it.
3. I noticed that there was some delay between the lock screen and start screen getting loaded. But this has disappeared since yesterday.
3. On Sunday, I had some time and tried reset phone to reset the phone which brought back my SD card.
4. After resetting the phone, I tried installing various apps through store update. Noticed that store application is very slow to load and usability has to improve. Also, had hang problems thrice when trying various installed applications. Looks like there are still issues in task suspend/resume probably in 512 MB devices.
5. Much of the applications don't exit and they stay in background requiring us to close them manually.
6. Messaging application: If I delete a conversation thread, since all the messages are deleted the screen goes blank. I thought it is going back to previous screen. But nothing happened. Then I pressed back button to make it go to previous screen. Looks like some minor usability issue.
7. When I tried opening the mail application today, again the mobile froze and I had to reboot. After that I was able to use the app.
8. Still some applications take time to open showing Resuming message. But performance seems to be better than previous build I tried.
9. Battery life seems to be as good as in 8.1.
10. Didn't try edge much. But seems to be fine.
Overall it seems that the build is really good but it will take more to become a stable build since hang problems are still there. Probably with 512 MB devices, more performance improvements are needed to prevent hang problems (My 8.1 rarely had hang problems). Store application also needs to improve.