Ukraine border was no worse (or better) for me than any others, although it was the first place anyone noticed I'd been using photocopies instead or genuine documents for my bike. I spent an hour or so entering, less departing, and no one checked my (lack of) insurance. Moldova is worth at least a quick look around; be sure and get out on some back roads so you're forced to navigate little wet, steep tracks, get lost, search for teenagers who speak some English, etc. Speaking some Russian would surely have been helpful, but in the end it all works out.
It took longer to enter Moldova than elsewhere, largely because I missed the insurance station which was, for no apparent reason, on the Romanian side. They sent me back, then made me wait in the queue for a second time. In the rain.
Edit to add: and of course petrol stations in Eastern Europe are as varied as they are in Western Europe. It'll all be readily apparent. I did get some bad gas in southern Poland, causing me two days' delay and a lot of consternation, but that could have happened anywhere.