My first time trying the 730/2s today - I tried both Standard and Ex-First Class (can you call it that if it’s never been first class?) As many others have said, the seats are definitely harder and the (faux?) leather headrests are not as comfortable as they appear. The interiors seem bright and airy with a very similar feel to 720s.
Acceleration is very impressive with us easily able to make up time on the 350 schedules. I found that cabin pressure in tunnels felt much heavier than I remember in the 350s especially Kilsby Tunnel. Whilst the interior did get louder as we reached 100MPH, I didn’t find the riding sound to be any louder than the air conditioning.
My only criticism so far is the location of the info screens, whilst this is also the same in the 350s, you don’t always have visibility of a screen depending on where you sit.