I've been playing some, first as Germany building right up to war, after that I played some hands-off games to watch the ai (playing as a small country in south america and toggling fow). It's been... a mixed bag. I won't go into everything, just some of the stuff that stands out.
First the good -
Industry and trade - I like the way industry and trade are managed. It's easy to see what you have and what you need. Any resource shortage triggers a notification.
Division designer - You can really personalize your divisions, making huge ones or small garrison divisions. There are templates but you can do what you want (given you have the land experience to change them).
battleplan system - You can just use it if you want, and the ai seems competent enough at filling out a front at least. So if you don't want too much micro you can give the ai some direction and it will do ok (this is for a defined front only, more on that in a bit). The general opinion so far seems to be that the best compromise between battleplan/ai and full micro is to just manually control the breakthrough force, and let the ai manage the mass of the infantry.
AI - Well, it certainly does perform naval invasions, as opposed to the last game where there were few.
Supply - Well it's certainly simpler than the last game.
Now for the bad....
AI part 1 - It performs too many naval invasions. As in, way way too many. Some examples from my current hands off game - When Germany declared war on the Netherlands they decided the best way to stop the German horde of soldiers was to take a good portion of their army and invade a few provinces up the coast. It didn't end well. After France fell the UK had at one point 3 different landings along the German controlled coast, along with one in Italy that had been going on for over a year. The UK lost many divisions in these landings. Germany was not yet at war with the Soviets, so it was probably unwise to spam landings. Oh, and South Africa decided to land a force in the German homeland, by themselves. So basically it seems that the ai cannot evaluate the odds of success after the initial landings, even against overwhelming odds. Thus they can end up wasting their army on them.
No beaches - So yes if you don't want them to establish a beachhead you have to garrison nearly every coastal province. Though they do need to get to a port for resupply.
battleplan system - Given the above you would think there would be a way to let the ai manage the coast right? Nope. You can't set a coast as a front. One work around is to draw a fallback line along the coast, but the ai won't respond if it's breached, at least from what I've seen. Garrison doesn't seem to the job either. This is one place I really miss notifications.
Historical start? - Well it isn't nearly as historical as you might want. My current hands off game had Germany decide to flank the maginot line by going through Switzerland.... There have been some really weird results I've read about on the forums, though at least some of them appear to be primarily the result of the sometimes brain dead ai.
AI part 2 - A few things. Why does the ai fight over the Sahara? The response to naval invasions isn't consistent. Germany seems to consistently beat them back, while I saw Italy almost ignore a large UK landing north of Rome as most of their army continued to try and push into southern France. They eventually dealt with it, but that may be because the UK got distracted with other invasions into Germany. And fighting over the Sahara.
Germany seems to have trouble at times with Denmark. There have been some screens of Germany having over 100 divs just parked there, either unable to conquer the last of the provinces of Denmark, or across the strait into Sweden if at war with them.
Free military access if you have a common enemy, no permission required - Now this is one thing that just baffles me. If you and another country end up at war with the same enemy, they can just march troops all over your territory, and you can't stop them. Unless you go to war with them, that is. For examples of this I would suggest reading the forums, but here's one. Say that you are Germany, and at war with the allies but not with the Soviets yet. By some weirdness the Soviets end up at war with the allies. Now you will likely have Soviet troops all over Germany, defending your coast, and going to any front you have with the allies. Something like this can happen with any set of allies or enemies. I would like to know how this got through testing, though the cynic in me would say they likely spent all their time playing multiplayer :\
Now there will be patches, the ai will improve, and I would bet that the mil access issue will be changed. So I still wouldn't say don't buy it, but it wouldn't hurt to wait a bit, at least for information on patches. If you do want it now at least do some reading and watching videos.
Also if you do play it, save frequently. You may want to load from a save if any ai craziness occurs. It's not fun to play as the US, for example, and spend all that time building up, only for something weird to happen giving you little to do with your forces.