Yes

Never played it, though (or because??) I love the "Might & Magic" franchise.

Well, then here's another one for you folks (quite simple, I guess):

The hero of this game...he never changes.

That's the only thing I dislike about the game. Why make it a Might and Magic game, and then make absolutely no references to the Might and Magic world? Had it just been called "Crusaders" for example it would have been a decent linear action hack n slash game.
This, plus the hype and the rush to get the PC out together with Playstation (the PC is unpolished at times) is probably the reason why it wasn't so well received.

Is he human?

Planescape: Torment?

He looks human-like, but he isn't a human being.

No, it's not "Planescape: Torment", but both games have a similiar atmosphere.

Is it an RPG like Torment?

What's the hero's job/profession?

It's an action-adventure with a linear narrative (though backtracking can be very useful) and some RPG-elements (no experience points or character levels/classes, but perks to find and buy + some inventory management).

Is the main character a vampire?

His goal is to prove his innocence (they insist at the council, that he is responsible for the annihilating of mankind).
No...he doesn't drink blood, but collects souls in different colours.

Hmm defiantly not Raziel from the Soul Reaver series then? (pretty sure he and Kain are supposed to be vampires, of a sort...)

It's not Raziel, but because of similiarites, the game we are searching was often compared to the "Legacy of kain" series.

War never changes so the answer is... Darksiders

Shadowman then?

Correct!