I thought it was OK, just OK. I don't feel it really matches up to the HST, for which it was supposed to be a replacement. The HST is an astoundingly good train and hard to live up to. I may be biased in my affection for them as they are what I've grown up with.
The seats seem a bit mean in terms of padding, although it would be fair to do a long journey on them before passing final judgement. Yesterday I just did Didcot to Paddington.
The lighting is not as horrible as what they did in their HST refurb - not the deathly blue - but I felt it was a little too bright. Harsher than in a Pendolino or Mk4.
The general finish feels just slightly on the cheap side. My suspicion is that in 5 years time they'll look a bit bashed up and everything will be a bit rattly like in a Voyager.
It does feel *a bit* more spacious than a Pendolino.
Not exactly quiet. I sat in a carriage with motor bogie deliberately. The diesel turned off just after we left Didcot so I only heard it in idling mode. It did seem less noisy than in, say a Voyager, but dunno about when it's under full power. On the electric there was quite audible motor noise. I felt more so than in a Pendolino. In non motorised coaches there was still a fair bit of noise coming from the AC etc.
On the electric it certainly can move, with acceleration notably greater than in an HST. Good for timekeeping of course although I felt there was a bit of a lurching ride, also during deceleration. In general I felt the suspension was a bit harsher than an HST/mk3.
I don't like that there's no buffet car. It doesn't feel like a long-distance train. That was my feeling overall; doesn't feel like a long-distance train which is what it was supposed to be. I think I'd rather do a long journey in an Electrostar than one of these. However - I'm not up to date whether the variants serving Penzance etc will be different (this was a Bristol service).
I don't like that a 10-car train is two 5-cars coupled together with no access between them. I just don't like it conceptually. And it seems to waste a load of space in the middle that's taken up with drivers' cabs that aren't used.
Constant automated announcements are as unwelcome as on any modern train.
For me the loss of droplights is a big deal; however, I guess it's inevitable and for most people a non-issue.
So I will continue to seek out HST services for as long as they remain. Will be interesting to see if the East Coast 800s are much different.