I haven't played any of the previous Disciples titles. Maybe that's my advantage, because so far I like it.
What you certainly should not expect is a challenging strategy game of the good old days. This is a dumbed down version with a lot less freedom and strategic variety and you possibly will play the campaign only once and possibly never touch multiplayer at all because the game does not really allow enough strategic options for that and the gameplay by itself is not as compelling.
That said: what you should expect is up-to-date graphics (with a darker theme than the Heroes series), charming musical themes and a nice story with some twists. The story itself is not new I'm afraid: fallen angel trying to take over the world (again). To do that the dark overlord needs a "Mc Guffin" that in turn everybody chases after. That's it.
Same old story of the devil taking over the world that has been told so many times now that it's hard to tell which game is a rip-off of which. However: it's nicely told and has some compelling bells and whistles and twists.
Three factions are available in three campaigns that build up on one another. Cutscenes (so far as I have seen any) are rare and are mostly zooming in and out of hand-drawn black and white still-images with (really good) voice-over.
Over all the game will keep you busy for a few days.
It's not brilliant, it's not perfect. But if you are looking for an entertaining, easy-going distraction with simple (not too complicated) gameplay, it is worth taking a look at. If you are a looking for any more than that, this game is not for you.