The first campaign, Tiger Ace, is a feel-good session of destruction and mayhem with increased power gathered from Commander points, which the unlockable skills tie in with the gameplay well. Having said that, the first 2 campaigns play like Warhammer: Dawn of War II, conquering the maps with Hero units mainly and ignoring unit building and resource management, which is quite welcome from the frantic micromanagement in the first Company of Heroes.
The third campaign then brings back resource management and throws you with insurmountable odds, which is clearly more challenging but sort of a downer in my view. Sometimes you can just watch in dismay for 5 minutes at the wrong move you made and reload, ha. Nevertheless, play at Normal mode for the final campaign and you would be just fine and take things as they come, it will still be ridiculous :)
If there are any new units, they don't make much of an impression to me or to the game, except for the Hero units. Though in the end, it is still the consistency of the high production value of the series that made me enjoy Tales of Valor.