Very important. My personal choice is that it be served deep orangey-brown, with sugar, and you should be able to stand a teaspoon up in it.
Just googled to see if the milk thing was an aristocratic or plebby thing. Apparently, the milk went in first in the 17th and 18th centuries, because the china cups were so delicate, excessive heat would crack them, so the milk cooled the tea down.
For flavoured teas, like Earl Grey, Lapsang Souchong, etc., no milk is required. However, if that's what rocks your boat, then fine!