OK here's my review after some testing:

Unlocking the bootloader and flashing Sailfish worked flawlessly after I struggled a little bit with the two different boot modes of the Xperia. The new message booting the device that the bootloader is unlocked is really annoying.

I inserted the SD card from my Jolla 1 and restored the backup with no problems.

The UI response is fast and multitasking many programs is clearly better now thanks to the 3GB RAM.

I tested Bluetooth with lots of different units and profiles. The only device I found not working was my car don't play music with A2DP.
Interestingly HFP works. But this problem I also got with the latest firmware versions of the Jolla 1.
WLAN on both bands work but using static networks the first time fails to connect. But again the Jolla 1 has similar problems.

Telephony functions like voice calls, SMS, MMS, and 4G work out of the box. Only tethering is not working as expected.
The build in browser is fast enough for me but here's surly some room for improvement.

Alien Dalvik seems to have a little better compatibility compared to Jolla 1. I successfully used some programs which have flaws on the old Jolla like a new Here map.

As for many people the camera seem to be an important feature I took a walk and some photos:

http://www.sbock.net/upload/Sailfish Picture 1.jpg
http://www.sbock.net/upload/Sailfish Picture 2.jpg
http://www.sbock.net/upload/Sailfish Picture 3.jpg
http://www.sbock.net/upload/Sailfish Picture 4.jpg

Too bad the sky was very overcast but personally I'm quite pleased with the result. Clearly extremely better than Jolla 1 but of course this is no real achievement ;-)


TL;DR: I'm happy with the hardware and the current state of the software. Good job Jolla team!