I'll be in Berlin for a couple days soon and I'd like to see some DDR stuff while I'm there.
The DDR Museum looks interesting, even if it's just to look at the visual representations of everyday life while ignoring the lib remarks on Stasi oppression and whatnot.
The DDR Museum is actually cool, it is mostly just a lot of finds that were unique about everyday life in East Germany. There are small lib exhibits about prison, the Stasi, and the Berlin Wall, but these are stuffed away in the corners and no one cares about them. People go there for the Plattenbau replica, the Trabant and Wartburg cars, and the thousands of collector items. Be advised though, it is packed.
Absolutely do not go to the "Cold War Museum" that promises to tell "two sides of the same story". It doesn't, it's expensive as hell, there's barely anything in there, and you have to scan QR codes to see what the exhibits are about. You can have a lot more fun in the Espionage Museum and the Deutschlandmuseum.
As a communist, it is mandatory that you go to the Soviet monument (Sowjetisches Ehrenmal) in the Treptower Park. It was built by and in commemoration of the Soviet soldiers who fought against fascism in the Great Patriotic War. Just a few metres outside, people go running with their dogs, play annoying music, and have picnics. You enter the gate and you are suddenly in another domain, the weight of history overwhelms you like an invisible wall. It is a place of calm, where only the sound of willow and poplar trees rustling in the soft wind breaks the silence. It is a place of rest, mourning those who gave their lives to liberate Europe and honouring their remains. But it is also a place that celebrates victory, with its giant statues and the two red granite flags, the white sarcophagi inscribed with golden quotes of Stalin in Russian and German, and the triumphal mosaic atop the burial mound.
If you wonder about the location well outside the city centre, it is because Treptower Park is also the place where the already-banned KPD had their secret final meeting in 1933, inside the Archenhold public observatory. This is also a good place to check out if you are interested in astronomy, given that it has a small visitor centre with a free exhibition and that Einstein gave his first lecture about General Relativity there.