Kirsts' books are good, but they're very much like Bernard Cornwell's in as much as they're very similar characters, or so I thought. There'll be the ardent, comitted Nazi (1) with few if any redeemable features - usually the main antagonist; (2) the officers who fight for the fatherland but have no great love of Hitler, but carry on because they always have; (3) the rebellious and pretty young girl who goes against her parent's views (i.e. usually is sympathetic to the allied cause); (4) an enemy of Germany who might work with the protagonist because they are more interested in some higher cause despite their being ostensibly on opposing sides; (5) a fat, genial person (usually a corporal or Gefreiter), who is more interested in surviving - not a Nazi, not a freedom fighter, one who aims to amiably amble through the war in as much relative comfort as possible; and finally the protagonist (6) - usually some skilled individual who is patriotic, but hates Nazism, and will fight to bring down the regime, and save those who they care about regardless of risk.
In a similar way, Cornwell's books have characters who are very similar across his books in all but name and setting.
Don't get me wrong, they are good fun books, but something of a product of their time and, as one might expect, they take a certain attitude that was very prevalent in the first few decades after the war in Germany. There are very well written, and quite funny as had been said though.