I think in real, practical terms, the main complaint that can be levelled against them is that they weren't long enough
They also have one big plus, in that the PA is an actual live person, and you're not treated to a great long recital of automated messages of carying usefulness.
They aren't better than HSTs. but they are damn near as good.
You know, I've never found the Smelly Toilet Problem a problem, or it may be that I just don't find it objectionable. At any rate, i don't think i've ever found it worthy of complaint.
besides, I like rumbling and vibration under my seat. it's the sound of power! Particularly when it opens up sweeping through a station.
I commuted on them making a 1h 15m journey each way to and from Birmingham for 6 years. To be fair I made a conscious effort to avoid the busiest trains. Overall I found the overall travelling experience superior to FGW HSTs which I had been using before for a similar journey length to London. Being over 6 ft tall I always make for the priority seats with the additional legroom. They are located at one end of each coach in standard class. The smelly toilet issue has always been there, but in my opinion you need an acute sense of smell for it to be a problem in the passenger accommodation.
I have been on Voyagers countless times, and the only criticisms I have of them are the toilets can be a bit smelly sometimes, and there doesn't seem to be a sensor on the vestibule doors so they shut on people sometimes. They are very nice inside, especially Virgin's ones with the shop, and the hate they receive was more down to the haphazard way they were introduced by Virgin (whoever thinks XC is bad now, remember how poor it was when Virgin had it. 8 car trains should not be replaced by 4 car trains Virgin West Coast is very good, but they ruined XC and deserved to lose it. Arriva have been much better). The seats are far better than IC70 seats. They aren't better than HSTs. but they are damn near as good.
I'm not sure that can really be put down to reliability!
Unless there is some magical kind of obstacle repulsion system which was not functioning!