I've been playing Disciples II for a long time before I found some good offer on the following chapter: I've played Renaissance, Reincarnation and Resurrection.
Although Reincarnation was the one I enjoyed the most (but also the first I played), I have to admit I found Renaissance to be quite easier. And that appears quite strange and opposite compared to all the reviews I read on Steam.
The big flaws of the game, in my opinion, are three:
1. the fact you can't decide whether to attack or retire from a battle when you come across an enemy;
2. you can't use shortcuts (at least, I'm not able to use them on Renaissance while I used them all the time on Reincarnation);
3. battles can be a bit confusing if you don't pay attention when deciding every move: for example, if you click on an hex too far from your player he will go there on the next turn, but you can't set him on defensive status.
Moreover, I didn't like the fact that range attacks can hit everywhere on the map, even on most distan hexes. I way prefer Reincarnation battle mode on this sight.
Also, it's never clear which charachter got a level up, there's no sign to notify your hero can learn new abilities and so on.
All in all, I'd surely suggest Disciples III - Renaissance to anyone fond of the Disciples trilogy, but if you want a more challenging, refined and precise game experience then you should definitely go for Reincarnation.