I think everybody — Ukies, Russians and Americans — assumed that the Russian armored forces would have been more successful at break-thru and encirclement than events later proved. Everybody was wrong about how the war has turned out thus far.
The Ukrainians created Maginot Line-type fortifications in the populated portions of the Donbas over an eight-year period. I've heard that the houses in that area are very solidly built, unlike the stick construction that us Americans are used to
Once the militias have cleared those, the way is open to the Dnepr.
Russia attacked during the spring mud season, little chance of success when armor is restricted to modern roads.
Now Ukraine is on the move with the fall mud season about to arrive. Should be interesting.