I was in Ukraine last summer. I assume you're aware of the political tensions between the two countries. Pick your crossing point between Russia and Ukraine carefully, the further west the better. Ukrainian roads on the whole are barely ok, you really have pay attention to such things as manhole covers ( missing, or the grate so far apart that anything narrower than a motorcycle will fall through). The largest city I visited, Lvov, was practically unrideable, the cobblestones being in such bad state. There is no bicycle infrastructure, so don't bother looking for bike paths.
The upside is that the people are really friendly, excellent quality accomodations are ridiculously cheap, border formalities are painless ( if you have the right passport) , and the natural and cultural landscapes offer endless possibilities...oh yeah and the beer is good and cheap.