Crimea is a recognized part of Ukraine.  Just because Russia had Russified the region before doesn't mean that the territory can be simply annexed by Russia.  It was all a ruse put up by Russia claiming that Russian speakers in Crimea were being put under the thumb by Ukraine.

Using their little green men to invade Crimea brought the international sanctions against Russia.  There was no provocation against Russia by Ukraine until the annexation of Crimea.

Russia could have acted more friendly to its neighbour and secure another long term lease on their port.  Now, it has essentially burned any bridges for the future with Ukraine.