Given the relatively small number of troops, the decision to do a broad front advance just made everything worse. It meant that they couldn't really get local superiority anywhere because they piecemealed out the limited troops they did have.
What made it even worse is that by attacking Ukraine from the north, south, and east, the Russians created incredibly long exterior lines for themselves. Impossible to quickly reinforce success, whereas the Ukrainians have much shorter interior lines to prevent breakthroughs. Add to that the spring muds making the shifting of forces even more difficult, and the Russians handicapped themselves right from the start.
Once could say it is like punching an arm into the ocean...quickly the whole arm gets enveloped. These extremely long exterior lines....static lines at that....are completely open to ambush and attack. Additionally, the failure to coordinate a combined arms approach has added to it. In many ways, this is almost like Operation Barbarossa in reverse. The milestones have all been missed. At some point, the enemy is able to regroup and counterattack.