For me I have travelled many time in sleep-trains in the post soviet countries.

Provided you are in 2nd class or higher, the sleep is generally comfortable and lulling. But I might be used to it, as we also did often when I was a child and I was used to rocking and train noises.

Same experience, walking around Lviv at 7am, until I finally had to buy a hotel room just to get a 2-3 hours of good sleep and then check out again.

They must have thought we booked that room as a "love hotel".

I took several night trains in my life (Prague-Warsaw, Prague-Tatras, Wien-Venezia, Prague-Frankfurt) and while the experience is interesting, the shaking movement of the train underway plus the freaking loud station loudspeaker announcements whenever you arrive somewhere resulted in very bad sleep. 2-3 hours at most.

Also short beds. I'm not freakishly tall, so the bed was missing just a few centimeters, but combined with the other factors you mentioned it wasn't a great time.

Yeah :( I remember being on the night train from Munich to Vienna and the bed being only 180cm or something. Though I had booked the cheapest sleeper option that was available (sharing the room with 5 other people), so maybe this is different in the upper classes?

Do you always sleep with your legs stretched out?

Come to think of it, I actually do. But of course if you don't then you won't have problems with the length of the bed.