Elven Legacy is good, but really hard if you go "I want all gold victories".
The expansion are really good, and a little bit easier but still hard.
The thing you need to know are the effects of perks in game. Some of them are must-have and others are situational. A battle can be hard if you didn't wisely choose your perks.
If you liked Fantasy General, take Elven Legacy WITH its expansion because they really add to the game.
And it has nothing to do with HoMM : EL is just a combat simulator and a real good one.