Large parts of our trip to Asia is on the famous Trans-Siberian Railway. It goes from St. Petersburg in the north-west of Russia to Vladivostok in the far south-east and has several sideways like the Trans-Mongolian line and the Trans-Mandshurian line to China. I started my Transsib-trip in Moscow and am currently in Ulan-Ude (Улан-Удэ).
Travelling in middle-Europe, one is usually not used to several-day long train tips. On our trip, we used only Platzkart (плацкарт), which is the 3rd and cheapest class which has a bed (on some parts you can get seat only tickets, which are even cheaper, but we always travelled over night, so this was no suitable option). Platzkart means that you're not travelling in small compartments, the whole carriage is one compartment with several beds in it. Although we read in several travelling guides that it's an uncommon option for European travellers, we found it quite satisfying.
Every carriage has usually two train conductors. Something common on russian trains is that you can always get hot water to make tea or packet soup. I read in advance that there are a lot of food facilities on the stations, but this turned out to be much less of an option than thought. There are usually only small kiosks which all have more or less the same offerings.
Our longest train-trip was from Yekaterinburg to Irkutsk, which took us more than two days. It was very exhausting and we plan to avoid any more train trips longer than 24 hours for the rest of our journey. We also had some unpleasant experiences with drunken fellow passengers.
Update: What I forgot to mention that's very noteworthy: On our trip, the transsiberian train was always very sharp on its schedule, at maximum it was only minutes behind. Very remarkable for several day long train trips.