The interior doesn't look too bad. It's good that FGW have retained the units' original seats instead of fitting Richmond or Chapman seating (both of which aren't especially comfortable IMO) since the original seats are perfectly adequate, although it's interesting that FGW have chosen to retain the original 3+2 seating layout.
SWT decided to change the seating layout from 3+2 to 2+2 in its refurbished 455s and create more standing space following passenger research which indicated that not only do passengers not like sitting in the middle seat, but passengers prefer to stand for short journeys.
The refurbishment of the 165/6s does not appear to be as comprehensive as SWT's refurbishment of its 455s, so perhaps FGW decided not to make any radical changes to the interior design as a result. I prefer to have a seat regardless of the journey time (which is why I don't like the longitudinal seating layout of the 378s), and I don't mind sitting in the middle seat of a 3+2 seating layout, so long as I get a seat.