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The Dwarves are all familiar units, and the only new one is the Erdlord in the second tier (but he's also an old unit). Among the alternative units for the Dwarves, only the Bears stand out.
For the Humans, it's the opposite – all the units are new, and the Inquisitor and Archangel show promise, but otherwise, everything is in red.
For the Elves, all the units are new except for the Dragon and Ent (the Wild Ent loses defense, making it die faster, especially in large battles).
I also didn't like the alternative units for the Mages (the Gremlin is only useful in battles against other Mages with Golems or against heroes with strong ballistae, like Dalek; the Elemental Gargoyle dies too quickly, and the Golem has the same problem, and Endless Retribution is more useful; the Mage, Djinn, and Titan also don't impress with their abilities – the old ones are better; the Kshatriya is the only one I liked, as the Whirlwind is visually appealing).
In the Inferno, all the units are new except for the Imps, Demons, and Archdevil, and I also slightly prefer the old Cave Lord.
For the Dark Elves, I liked the idea of invisibility (but it's very easy to dispel), but it's great against neutrals (especially against archers), and the old upgrades are still the best.
The same goes for the Necropolis – only the old units are used in battle, except for the Lich and Dragon.
As for the Orcs, I understand them. There's a choice – combine and think; there's no constant here, it all depends on the situation. :D