The immediate goal is overthrowing the current regime in Ukraine. That much is obvious. Beyond that, nobody really knows. At a very high level, Putin wants to

The immediate goal is overthrowing the current regime in Ukraine. That much is obvious. Beyond that, nobody really knows. At a very high level, Putin wants to maintain a buffer zone between Russia and NATO. Russia doesn't have the resources to occupy and/or annex Ukraine, at least not in the long term. Putin must know that. He can't hope to install a stable puppet government, because Ukrainians would overthrow the puppet in a revolution. He must know that as well. Maybe Putin wants to cripple Ukraine permanently. Take Odesa, and Ukraine loses access to the sea. Take control of enough territory that it doesn't matter what NATO and the EU will do with the remaining Ukraine. Or maybe Putin has become an idealist instead of the pragmatist he was. Maybe his actions are now guided by beliefs rather than expected consequences. If Putin believes that the former glory of Russia must be restored by any means necessary, he may drive Russia into ruin by pursuing that.