My copy arrived today and I ran through the tutorial scenario in right around an hour -- 4 turns, would take me much less to replay it I think. Not to fear for the hardcore Grognards though, the Greece and North African campaign seem much larger.
There aren't any major changes in the core HPS engine, but they have made a few improvements overall -- you can see a rough estimate of attack odds before committing to a battle, for example. There are a few hotkey hints now instead of none.
But overall the biggest improvement for me is in the overall game design. It is much higher level than the Panzer Campaigns games -- 10 kilometer hexes, 2 day turns, and the system is accordingly a lot more streamlined. Stacking limits keep you from putting more than a divison in single hex and in general there are way fewer stats to keep track of (though the core AA, AT, attack, effectiveness, etc. are all there). The divison + brigades unit sizes are a bit easier to process as well though they aren't as well visually represented as I'd like.
As someone who just likes a lot of the geography aspect of these games, it's also nicer to play at a scale where you can actually see some recognizable bits.
Anyways, mark me as pleasantly surprised with this one. It's no War in the Pacific, but I'm digging it so far.