In the Name of the Tsar adds in six new maps (including the already released Lupkow Pass), new weapons, new vehicles, the Supply Drop mode, the Hussars, and the Russian Army. Yes, the entire Russian Army.
In addition, this update will add in HDR support to Battlefield 1. Specifically, it adds in HDR10 support, the new hotness in visual eye candy for those with supported televisions and monitors.