I would have loved to have travelled the Trans-Siberian/Mongolian while the USSR was still in one piece, as it would've been something else to have experienced that, although perhaps slightly voyeuristic, being from outside it!
I can recommend Paul Theroux's various books on the area, long time since I've read them but I recall both being a good read and written when communism was still strong and Western influence slight - The Great Railway Bazaar (Trans-Sib), Riding the Red Iron Rooster (Trans-Mongolian), he re-traced these journeys in 2006, writing Ghost Train to the Eastern Star, which I've not read.
On my Trans-Mongolian trip, I met two distinct types of Russian people. Young people (under about thirty) were more than happy to make friends and converse with you in English (I did try my very sparse Russian), but the older people were a little more reticent - probably a throw back to the old USSR I guess. The leg from Irkutsk to Ulan Bator was quite surreal - with, what I can only assume to be 'smugglers with the blessing of the rail staff' openly operating
Having done the Trans-Mongolian, I would like to go back and do the 'Trans-Manchurian' - which is Beijing to Irkutsk via Harbin ('round the back of Mongolia') and then complete the rest of the Trans-Siberian out to Vladivostock, but the current political climate in Russia (plus a slight lack of cash!) is putting me off for the moment.