Tanya the Evil (the anime) is fantastic and I love it. Tanya the Evil (the character) is terrifying. She's a little girl who used to be an adult male salaryman in her past life, working in the kind of Human Resources role that should probably be called Black-Hearted Torment. One of his victims pushed him under a train. Now she's a commander in a fantasy parallel universe version of World War Something (in 1926), fighting for the Germans with almost inhuman efficiency, a screaming black void where ordinary people might have "mercy" and "compassion" and lots of hilariously evil faces.
It's an evil protagonist story, obviously. This is fun because:
(a) you can't say Tanya doesn't get things done. She's dynamic, to put it mildly.
(b) she's probably the cleverest person in the world, at least when it comes to war and killing people. (Being X would presumably be cleverer, but is He a person?) It's always satisfying to watch intelligence at work. Some of that's time-twisty foreknowledge from Tanya's native future, but mostly it's just being psychopathically analytical and capable of taking a cold, long view of any situation.
(c) her enemies sometimes deserve it. Here she lets rip on Stalin's Russia.
(d) her faces.
(e) Being X trashing her plans. This is always hilarious. It's the best thing about the show (although I like her appalling radio declaration in ep.5 of the TV series too). We like watching Tanya, but it's always even funnier to see fate tormenting her. She'll have everything worked out... but then Being X (whom she refuses to call God) will take a mighty dump and send her back to the worst hell on Earth. This will only stoke her hatred of Being X.
Anyway, this film's set after the TV series. Tanya and her 203rd mage battalion are on the front lines in Africa. (Among her enemies is a Charles de Gaulle lookalike. Don't expect him to live long.) Tanya does her Tanya thing, e.g. "slaughter them to the last man!"
Then, to her horror, she gets redeployed.
It's Russia. It's freezing and inhospitable. It's ruled by a Politburo that's liable to have its own members dragged out by NKVD thugs. The one who tends to make the real decisions isn't actually Stalin, though, but a fat, slimy paedophile with a birthmark on his head.
Tanya despises this regime because she has a well-informed capitalist libertarian's view of Communism. Of course she'd cheerfully massacre innocents of any nationality, but here she's also running mental projections based on her knowledge of the Soviets and their military. Oh, and Germany isn't at war with Russia (yet), so she's breaking a treaty just by going there in the first place. Guess how much she's bothered about that.
This isn't a complicated film. The plot's well constructed and satisfying, but the formula is pretty simple. It's a war film. It has an evil protagonist, yes, and a semi-epilogue where Tanya's taking the long view and predicting the end of the war... but still basically a war film. "Slaughter them to the last man!" Tanya's so hard to beat that she's liable to come across as a Mary Sue, capable of massacring almost any opposition, but here she's up against foes as scary as her, each in their own ways. One of those even has the name "Mary Sue". (Mary's a nice person, but with an almost uncontrollable desire for vengeance that makes her ever more unhinged and like a human superweapon. Tanya and Mary are almost the same person in a good/evil mirror. Note the scene where these two devoutly God-praising girls trash a cathedral and Tanya shoots the statue of an angel in the forehead.)
Is this a nice film? Nope. Is it a blast? You bet.