I have stumbled upon this movie accidentally when browsing through YouTube. I have never heard about it before and must admit, was quite impressed with its quality.
The movie depicts events from the first days after German invasion of Soviet Union on June 22, 1941. Unlike the well-known stories of the blitzkrieg, the movie depicts resistance of the Red Army encircled within one of the border fortresses. Brest fortress was attacked on the first day of the invasion, but it took 9 days for the Wehrmacht to capture most of the fortress.
There is not that much armour shown in the movie, but the battles are in my opinion very well depicted (especially hand-to-hand fighting scenes).
Historically, movie seems to be accurate as far as I can judge from the very little information available, though this being Russian movie, you will not learn about the years before the battle – German forces captured the fortress in September 1939 at the end of its attack on Poland (which was undertaken in cooperation with Soviet Union). According to the Non-aggression pact between Nazi Germany and Soviet Union, Brest and its fortress was later in 1939 handed over to Soviets. Thus in 1941 Wehrmacht had to capture it again… Wikipedia provides article on the 1941 siege here:
Full version of the movie with English subtitles can be viewed here: