The film is about the final 12 days of Hitler. It's not really meant to be a documentary or anything like that. It's a really good film and I was curious if these is any educational value to be had.
I actually used Joachim Fest's Inside Hitler's Bunker (one of the books the film was based on) for a class this past semester. As Fest writes, he composed the book off memoirs and recollections of the survivors of the bunker. However some things have conflicting reports, so in those cases he used his own judgement on what was likely to happen. However, I have not read Traudl Jung's memoirs, so can not argue it to that.
In regards to how close the film is to Fest's book, it's very accurate. While reading it I could picture specific scenes from the film, often closely resembling the book as possible. So if you are going for that angle, it is very well done.
However, it obviously is not a documentary or totally reliable. As I said, there are some details that have multiple accounts from survivors of the bunker (most notably how Hilter and Eva Braun killed themselves), and the dialogue is almost certainly not a perfect transcript of what was said. But again, I have only read Fest's book (and Speer's Inside the Third Reich, but that was a while ago so I won't comment in regard to that), which while one of the main books, is just one of the sources used, and at that Fest didn't include footnotes or anything, making it difficult to easily corroborate what he wrote (it is written in a different style than most historical books, almost like a novel). So in regards to staying close to the source material, it does a good job, so much that our professor told us to not use the film as a reference point in regards to reading the book.
Very. Not only did people survive the Führerbunker but people like Rochus Misch, Albert Speer, and Traudl Jung told their stories. Misch only died last September at 96 years old, and he was presented well in the film. He was consulted (I remember reading) for Valkyrie with Tom Cruise, because who better to get information on the Führerbunker from other than someone who worked in it?
A historian I know was interviewing Misch for a novel he's writing on the Battle of Berlin. As mentioned, Misch recently passed away, but my historian acquaintance was basically interviewing him up until his death. My acquaintance said he had gotten hours of documented interview information from Herr Misch.
Anyways, yes, the film is quite accurate.