Understanding German makes it more real. Some things do get lost in translation.
I have Trevor-Roper's book lying around here and read a few parts; Fest is also around (but unread so far). Basically, any book expanding on the entourage of Hitler in his last months makes it easier to understand the movie.

'Inside the Third Reich' (in English) is going with me on holiday next week. I hope to finish it within 10 days. I'm not sure what to think of Speer exactly. He refused orders in the last year or two, but before that... We'll see.