Updated opinion: I was wrong, but not.
I'm writing the following review as if I've done all the campaigns except for one, but more on that later.
Commonwealth: A very pleasant disappointment, the British campaign was the best. Unfortunately, the armors is not really good, but the infantry is, however, the sas units with the vickers machine gun and the 90mm cannon are brutal.
German: Everything is good, the infantry is reliable, the tanks are amazingly strong and accurate, the panther, stug III and tiger are awesomely powerful.
Soviets: The infantry is good, the machine gun is particularly effective, the T-34 is not so rough, the KV-1 is unpredictable when there is no chance against it, sometimes it is a zero, but the IS-2 and SU-2, and the ISU are very strong.
Japanese: Very good infantry, the tanks ones are mediocre, the machine gun is unfortunately not very good, it is more accurate, but slower than the others.
USA: They are definitely the weakest, only the rangers are strong, the sherman is overrated, medium trash tank, their infantry is not very good (20-round thompson, really..), their two best weapons are the Garand and the Bar. The Firefly and the Wolverien are the only good tanks. And I didn't finish this campaign because the game is unoptimized, it crashed and deleted all my saves. I'm sorry, but it must be my fault... but I won't give it another chance.
Other interesting things were the mind-reading (mainly German) mortars, the flying "ghost shells" over the tanks, the always-ready answer moves from the enemy.
Special things in the campaign by usefulness:
1. Artillery (Commonwealth)
2. Goliath (Germans)
3. Airbone/airstrike (USA)
4. Banzai (Japanese)
5. For the Motherland (Soviets)
Basically, it's not a bad game, I admit, and I even noticed that the more I played, the more I improved. It's definitely worth a try, but whether you like it or not, unfortunately I can't give it more than 3 stars due to its unoptimized features and bugs. This game is a strict teacher, but it can give you progress.