It initially sent shivers through the expeditionary force to Natal, because the Boers successfully held off Tommy Atkins at the Tugela and Wegkop against all odds. But in the end General Roberts arrived, did a massive flank march through the Orange Free State and the Transvaal, and at that point the war degenerated into persistent guerilla action by the Boers, and concentration camps for their wives, kids and servants. It started with the Mauser, but it ended shaking the empire for decades afterwards, up to the point where the UK empire was just a memory.
It provided a nasty surprise at San Juan Hill as well.