The most comprehensive and up-to-date academic military-history works on the Eastern Front of WWII are those of David Stahel. Stahel's work is more rigorous than Beevor's and provides a more in-depth, less 'pop-history' style discussion of the conflict. I've drawn heavily on Stahel's research and writings in my past answers, and fully recommend his work for any academic discussion of the military campaigns in the East.