Of course you can't really compare Herr Lehmann to dramatic history reenactments like Der Untergang.
But Herr Lehman is so full of comedy, but also full of authenticism and a plot not devoid of drama. It's dialogues are outstanding, but then the book the film is based on was exceptional to begin with. And the best thing is, if you like the movie, you will like the books. Sven Regener managed to show his talent in storytelling and humour in both art forms, book and movie. The connections he makes, the way he connects what actually happens to Frank Lehmann's thoughts is the best use of basic rhetoric means I ever saw. He doesn't use the "rhetoric artillery" so to speak, but achieves literary greatness nevertheless.
The acting is on par with the quality of the script though. Even if I didn't expect Christian Ulmen to do any good acting ever, he produced the perfect rendition of the lazy, slightly hedonistic, disoriented Herr Lehmann. Detlev Buck is outstanding as well, as is nearly everybody in the supporting cast.
10/10 for humour, artistic style, acting, all that while staying serious.