I personally found the original storyline more appealing than the expansions. It's more engaging. In terms of difficulty, "Hammers of Fate" is very easy. "Tribes of the East" seems to be the most challenging.

But it's definitely worth buying. If the full price is too high, you can get a collection. For example, I have "History of Two Worlds" – it includes all four and all five Heroes games. The quality seems good, with no major issues. But, as I understand it, you won't be able to play on Ubisoft's platform.