Take the Trans-siberian train

I had often dreamed of taking the Trans-Siberian Train from Vladivostok all the way to Moscow. I wondered how many people had already done so, could you please share your experience with us. I looked up and read stories about the trips which were made by people who had done so, and all I read was that they had very bad expeiences with the Russian immigration at certain borders. What is the real truth? Are they very strict on certain criteria of immigration matters? If not, what are the problems?