Imperial River Cruises has 20 ships sailing the rivers of Russia and one nuclear powered ice breaker that sails in the Arctic. The ships vary in size from less than 100 passengers to just less than 300. Unlike many river cruise companies, Imperial does not cater to English speaking guests so sailing with them will be a more cosmopolitan experience. They do offer English speaking guides and crew.
Accommodations - the 20 ships vary widely in size and age which means that cabin sizes will vary considerably. The older the ship the smaller the cabins are likely to be so, if you are sensitive to cabin size, care should be taken in the choice of a ship.
Itineraries - They sail the common Moscow to St. Petersburg route but they also do some things the others don't. They offer itineraries that sail all the way to the Black and Caspian Seas. They include stops at many smaller towns with opportunities for experiencing local culture.
Life on Board - includes nightly entertainment and lectures on history, art, music and culture. There are Russian language lessons and daily exercise programs.
Excursions - there are included excursions at each port. In some ports, optional excursions are offered which can be purchased on board. The purpose of all programs are to expose the guests to the culture and history of Russia.
Prices - for a mid level cabin will vary from about $250 per person per night to a little under $300 pp pn.
Sample Itinerary - Moscow to St. Petersburg