You mean other then the recommended unit size, composition, quality, and equipment that Bolt Action uses to make a balanced and historically accurate game?
We use Bolt Action for our WW1 games which latterly have been set in the Eastern Front. We use the rules more less as they are. Are far as I am aware most armies in the lists allow considerable variation in the size of infantry sections (from memory minimum 5 to 12 max). As for force composition and units quality, we usually go with what seems right for the scenario. Restrictions by the lists are more for competition style games.
To answer your original question, we like BA particularly for the pinning rule. Units take pins when taking hits (even if they save them). These accumulate (unless you take time out to rally them off) to inhibit your ability to give units orders. Sort of like a running morale status. It is quite a simple rule which has a realistic feel.
Not played Through the Mud and the Blood though they come with lots of scenarios adaptable for Eastern Front I would have thought. I also hear good things about Chain of Command. Again another WW2 set but I believe there is a WW1 supplement for them?