I remember a custom made Operation from CMBO times, I do not recall the name of the operation, but it depicted the 21st Panzer Division's attack against the invasion, the attack took place only a few days after the initial landings, and the whole of the division wasn't employed only 1 full regiment and parts of another.
Anyway, the operation was brutal, at first you star out with fully equipped units, good armor, good quality infantry, etc. The first phase of the operation wasn't all that bad, made good headway with few losses. By the 3rd phase of the operation I was facing naval artillery fire, Churchill tanks, AT guns, Fighter Bombers, etc.
On paper I had an entire regiment (in game yes, huge OP), by about the 5th phase of the Operation the size of my regiment was about 2 companies of men (I suffered huge casualties), and only 1 Tiger, and 2 PZ-IV operational.
For the 6th phase, I gathered all my men, and the 3 tanks and made one last push for a strategic hill overlooking the entire battlefield. Murderous naval fire 14 inch guns, overwhelming firepower and overwhelming numbers of the allies barely allowed me to even try and attack, but I did manage, just barely.
I reached the top of the hill eventually, with about 25 men and one PZ-IV. The Tiger was immobilized, but in a decent spot where he still provided fire support. The Operation was intense, and based on an actual, historic even of the 21st Panzer division's counter attack to try and throw the allies back into the sea.
In the end, I managed a draw, but in reality, it would have been a defeat. Sure, I reached my objective, but it cost me the entire regiment, and if the allies counter-attacked with the same support they had, they would have been able to eject me from the position with ease.
I am hoping for such OPs again.
There was one more OP I remember being intense and well designed. I remember the name of it, "We fight and die here". It was based on the 12th SS Hitler Youth division fighting in the Ardenne Forest.