By what I know of it the rank and file of German soldiery in WW2 wasn't really anything special. Oh, they were competent and well trained all right, but among the major participants the only ones for whom this does not hold equally are the Soviets. The grunts were just regular folks after all, not some kinds of all-conquering supermen; to get decent results out of them you had to use them properly, like any other soldier.

Which the Germans for a while did very well, having a bit of a monopoly on the whole properly massed mechanized units thing. Those were really their main trump card anyway - fast-moving, hard-hitting armoured formations supported by mechanized infantry and aircraft. Most of the infantry still had to leg it though, and German artillery wasn't anything to write home about - nevermind now entirely unable to keep pace with the mechanized units, hence the dire need for the "flying artillery" of the Luftwaffe.

And where this combined-arms trump card for one reason or another didn't work (be it due to supply issues or uncooperative geography, such as the vast dense forests in the Fenno-Soviet front or the ruin-maze of Stalingrad), the Wehrmacht seems to have had a bad habit of floundering. Or at least their rate of advance in "forest Russia" does seem rather pitiful (or, as in many cases, downright nonexistent), especially when compared to the breathtaking sweeps they could effect in the open grounds of "steppe Russia".

Bit of an one-trick pony really. Moreover the whole military system was really a bit too predisposed towards offensive thinking and constant movement - the focus on aggressive advance being obviously worth nothing, or even a problem, when faced with extended positional warfare nevermind now when fighting on the strategic defensive. It also resulted in an unfortunate willingness among the senior leadership to trade men for time - perhaps a necessary sacrifice for the Blitzkrieg principle to be fully effective given the tactical tools available at the time, but hardly one the Germans could actually afford on the long term as their entire world-conquest project rested on precariously thin resource base from the word go.

Pretty much the second the other guys picked up the whole massed armour and decent combined-arms principle, as well as the appropriate countermeasures, the Germans were screwed but good. That's the inherent problem in basing your overall edge on an innovative way of using tools everyone as such already has - the others only need to copy the trick, and the advantage is lost. And if you were relying on that advantage to overcome enemy superiority in other fields (such as raw resources)...

That the Reich was run by a bunch of loony idiots who didn't let the soldiers do their job properly and kept wasting crazy amounts of resources on technically impressive but practically useless "super weapon" schemes - not to mention the pure gratuitious waste of the Holocaust - of course did not help one bit.