It's better than Wargame: European Escalation, which on its own was already one of the best multiplayer RTSes out there.
The UI is improved, bugs ironed out, etc. etc.
There's a gigantic amount of units now, which is quite the statement when you think about how many unit types there were in the first game. Also, the new deck system is just leagues more in depth than the original system. You can choose to specialize in many different things. For example, you can choose to only use Canadian units (this gives you access to unique prototype units only the Canadians have), specialize in mechanized warfare (which gives exp boosts to mechanized units but reduces number of helicopters available to bring dramatically), and only use units prior to 1975 (which boosts the number of units you can field by 80%). Additionally, in the past whenever you picked a unit, you were forced to grab all the units in that tree as well as be limited to just how many units that tree allows you to field. Now you can pick and choose which units exactly you want and how many of them. So now my dream of having 60 sets of motorstrelki with BMP-1 is actually possible. You can also predetermine their experience level (which also changes how many units you're allowed to field).
There are about 10+ nations so you can see how complicated this can be. The battlefield can also get very overwhelming with the sheer number of different troops and how varied they are. I guarantee that the first few games you play this you will have no freaking clue what is going on as you wonder what a USMC Pathfinder is and whether it can actually take out that FAGOT squad with BMP-SP1 support.
Then there's the addition of planes, which just completely changes the way the game is played. Now you have fast, dramatic response to any incursion, which makes deep strikes into your territory so difficult to pull off. This means there's no real need to defend your spawns any more. Similarly, it's very difficult to actually attack anything if you don't control the skies. Furthermore, they just eat through any unit that doesn't have some form of good AA. Even lone AA is probably food. Improperly positioned AA batteries will also still fail. So everyone has to manage air superiority and AA cover. It's hardly overpowered though, as planes can't be fielded in large numbers and of course... they can't actually scout or capture territory. So they need you to actually see a target before they can do anything useful.
All in all, the balance is still great. They changed some things from EE that most people who haven't played it before probably won't notice. Things like how you now lose 80% of a squad if the APC carrying it explodes. Or the fact that you can field infantry in cheap 1pt trucks now if you don't want to buy the APC. The maps are also significantly larger to compensate for the amazing range of planes. And finally there are just so much more units on the field now. Hell, I have a PACT 1975 deck that has more than 240 tanks, in addition to all the other stuff.
All in all it's a great experience. The changes to maps so that you get mountains and actual varied terrain is nice too. It's 25% off right now with the preorder which gives you access to the extensive multiplayer beta. The only people I wouldn't recommend it to are those who are averse to multiplayer or RTSes in general.
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Edit: Ah. A warning for Wargame: EE veterans. Regular infantry are kinda shitty against tanks now. Eugen changed the light anti-tank weapons like Bazookas so that they only slightly hurt tanks and barely scratch heavy tanks. So the infantry rushes of old are kinda impossible now. You still need them though, as infantry are the kings of holding positions and moving through difficult terrain like mountains. Just you now need more dedicated anti-tank support to assist. However, Eugen also made all the anti-tank missiles more accurate to compensate. Similarly, flamethrowers don't travel 3km now either.