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I'll try to describe them all, starting with the original heroes (meaning, not from the expansions), and for now, I won't consider the storylines of the expansions (except for Godrick). (In general, most of the heroes, due to the lack of facial animation and the desire to show that the game has all sorts of annoying special effects, are very funny and irritating (it's good that it's much better in "Lords of the Realm")).
Isabelle - her face is sour, and her voice acting is just funny, with all sorts of "Oh, Nicholas, oh, they killed him" and so on. Although, mostly, her actions cause indignation, starting with the intro, when the king and the demon are locked in the church, and then they whine about how he's doing in there. And in general, it's not clear why the hell she went to gather a militia, to summon elves, and so on, because she became queen after marrying Nicholas, so why did she suddenly have to go to war?
Godrick - he's like a standard "for the light" knight, but his storyline was ruined. Take, for example, the deaths, where he lies completely unharmed, and at the end of the dialogue, he says, "I guess I'll die, because I need to create tragedy."
Nicholas - personally, all the Nicholas characters in the Heroes series are associated with running away to the circus (MM6 and MM9). He also dies strangely, he couldn't even defeat 3 horned demons in hand-to-hand combat.
Frieda - an item in Markel's inventory.
Agraal - something like the main hero of a popular fantasy Hollywood movie. Like the standard hero in such movies, he first throws away the Amulet of G, and then goes after it to the "center of the G empire." From the same series is his love for Isabelle. It's absolutely unclear how his geeting works, and in general, all the storylines are full of dislike for demons, which, in my opinion, is wrong.
Markel - also a fairly standard necromancer, but he has good voice acting and a good model. It's not clear why the developers let him get killed. I played as him, I leveled him up, and so on, but it just doesn't feel right. They could have made it so that we play as a good guy for the "bad" races, and another one gets killed, or let us play as a heretic or an elf who is ready to kill all the elves for, say, his stolen unicorn.
Railag - he turned out to be kind of strange. So, it turns out that anyone can come to the Elves, become the head of the clan, take over the rest, and go kill demons. Besides, all the ordinary elves have strange, wide ears (the worst design decision), and Railag's ears are almost sticking up, and he should have been kicked out of the elves just for that. He has as much charisma as Agraal.
Shadia - she's just average, but if you judge her as Biara, then she moves from one place to another very often =)
Fayden - well, maybe in English, in which the heroes were originally made, the poems sound normal, but in Russian, it's just terrible. In general, he has as much charisma as a log. At the end, he says, "Let's just kill her," and when he's refused, he doesn't do anything. Why was he carrying a bow with him (in the game, I never used it, I always created phantoms)?
Nicholas (vampire) - what kind of vampire is he? He turned out to be some kind of emo =)
Zeheer - the developers missed a great opportunity. They should have made him a rastaman who believes that he's riding a horse, but it just has slightly bigger ears than usual. Why did they even give mages a hookah? But instead, he turned out to be some kind of boring, standard-good, but kind of authoritative mage. (And why did he kill Markel? It's unclear, and in "Armageddon's Blade," Markel's skull also appears, so where did that come from?)
In conclusion, on a 10-point scale:
Isabelle - 2; Godrick - 4; Nicholas - 2; AgraalAG - 2.5; Markel - 8; Shadia/Biara - 5; Fayden - 2; Zeheer - 3; I'll give 10 points to the leader of the peasants from the first mission for the Empire, because they really shouldn't be fighting with some demons.
If I'm not lazy, I'll write about the expansions.