The features are different. Obviously you cannot speak of all Russians and Ukrainians, since a lot of people from Russia move to Ukraine and vice versa. And Russia is very diverse ethnically. But generally Ukrainians have broader features, are darker and just less Nordic in appearance. There was a large Jewish population and Greek ethnic population. Compare Margaryta Senchylo, for example, who is from the Ukraine, with Valentina or Vlada (both Russian). And Andriy Shevchenko the football player is fairly typically Ukrainian looking too.
Of course as I say, there is mixture and many differences within both countries. But ethnically on the whole, the ethnic make-up of the two countries is quite different. In Russia, the quantity of Nordic people (a racial type, which is generally narrow, slender featuers, very fair skin and usually blonde hair, as in the Scandinavian countries) is much much greater.