Some of the reason the twitter posts are mainly positive is that Alex Hynes/Scotrail/Hitachi etc are retweeting or quote tweeting only the positive ones they've come across which is understandable.
As an example, a guy on the 1st train to run in passenger service did about 8 tweets - 6 were positive and got retweeted, 2 were negative or slightly negative and didn't get retweeted.
The negative ones, 1 mentioned the seats being uncomfortable and hard and 2 mentioned the interior passenger display screens flickering if viewed from the side - I assume a bit like a video shows the destination screens flashing on and off.