One difference is that Hitler was pursuing his goal of German expansion into Eastern Europe, as outlined in Mein Kampf. Putin's motives are less clear. Is he trying to restore the Soviet Union? Is he working in tandem with the Chinese, the Iranians, and other Communist and radical Islamic countries to take down the West? Or is he just a madman?
Which is disingenuous, considering the history of ethnic cleansing in those areas, under Soviet rule. At least in the Sudetenland, the population was pretty much unchanged for several centuries, through Austro-Hungarian rule.