A decent review, but it leaves out a few of the key mechanics and aspects of the game situation that make this so successful as a game.
Overrun is just like ordinary combat but can be done during movement, as long as the attackers are all mechanized units (truck borne or better, so to speak), are all in one stack, and the defender can be approached from a hex that isn't in ZOC of two defending units. This makes for nasty, fluid, maneuver warfare possibilities with concentrated "fists".
Enhancing this effect, ZOCs are hard for leg units but soft for mechanized units. Also, any armor gives a column shift for combined arms (with an infantry also required, but that is easy), unless the defender has anti-tank capable units - meaning armor of his own or a few specialist ATG formations. There are also column shifts for effectively a unit morale or quality differential.
Next and critical, the German motorized divisions have 2 activation chits per turn, while the Russians all have 1 per turn (as do some German infantry formations in one of the two battles).
Add all these things up and the German divisions are terrors for all of the right reasons - flexible, mobile, unpredictable at where they were get to, etc.
But the CRTs can get bloody and attritionist some of the time. The Germans can't afford continual wear and tear on their main mobile forces. Much of their effect comes from hitting often and all over, but this magnifies the chances for and the impact of, losses to the spearheads.
Last, the Germans have an endless problem covering everything. They simply can't, if they are to keep concentrated forces for offensive maneuver. They in perpetual danger of losing their road LOCs and thus their supplies to flocks of Russian rifle battalions coming out of the woods from every point on the compass.
In other words, the game successfully models the asymmetry between the two armies, and the strengths and weaknesses of trying to make mobility and quality stand in for numbers.
There are a few aspects of the system that are a little too "fiddly" - the use of command points, rolling for artillery and joint attack coordination, and the like. Their game effect is good - to prevent factor-hunting to get predictable odds column effects, to add an extra layer of risk to battles, and to reward simplicity in tactics against control freak over-coordination of everything. It is just the implementation is a bit cumbersome - you can wind up rolling 1d10 4-5 times to resolve one attack (defender artillery support coordination, attacker artillery coordination, attacker ground unit coordination, occasionally air support coordination, then finally the actual CRT die roll... you get the idea).