If the Central Powers had won World War I (or a slightly later or earlier version of it), how would the Imperial German military have developed by the 1940s?
IMHO, it could go either way. It might be a force which is resting on its laurels, not the quickest to grasp the newest trends concerning equipment and tactics. But I cannot imagine it to become an un-motivated pushover force. Also consider that not all was perfect with OTLs-Wehrmacht either. It would be very far-fetched to assume that a Neo-Entente might beat this Germany within a few weeks.
On the other hand, Germany might have the strongest, best-led, best-equipped army and air force in the world. Maybe a bit weak on the armoured side, but then, if Germany wins WW1
without major tank involvement, then there might be less emphasis on this weapon elsewhere, too. Also, the HSF would be a force to reckon with, certainly among the 4 largest navies in the world.
Would OTL's field marshals and generals (such as Manstein, Rommel, Paulus, Guderian, Model, etc.) still be prominent?
Certainly as most of them had started to rise through the ranks already in WW1 - well, that is except if any of them catches a bullet ITTL WW1. Not willing to do all the work for you

I suggest you check the figures you are keen on in Wikipedia. If he lives a bit longer in this timeline (not unimaginable), Ludendorff might still be around.