This is one of the few unbiased and id-depth reviews of this phone, congratulations! I wonder what software version did your test units run. Asus has been consistently pushing updates that have improved the experience, adding some features here and there, reducing the battery drain, improving camera performance, etc. The early reviews reported bad camera performance and high battery drain, and thus gave it a poor score.
I´ve owned this phone for about two months now, and I cannot be more happy with it. Performance wise it´s great, comparable or better than many flagships, and definitely better than anything in it´s price range. Battery performance is average, but after reading lots of reviews of the current batch of flagships and midrange offerings, I cannot complain, as it fares really well, and has improved with software updates.
Most people complain about the button placement, but I´m one of the few that really like the power button on top, as it prevents accidentally pressing it. If you find it difficult t press it, just double tap to wake or sleep! Volume buttons took a couple of days to get used to, but also like it now.
As for the bloatware, I think it´s been exaggerated by most people. Yes it comes preloaded with some useless programs, but some can be uninstalled and others can be disabled. Some are really useful additions, like kids mode (better than some 3rd party programs I´ve used), app locking, startup manager, etc.
The Zen UI is the best non-stock Android UI I´ve used, I really like it. It´s pretty light and does not get in the way, unlike Samsung´s. As you can see in this article, even though the ZenFone2 has more RAM, it also has less bloat than Samsung S6 and Note 4:
http://www.techarp.com/showarticle.aspx?artno=897&pgno=0