Heroes 4 has many advantages, BUT: it has a terrible design (only Heroes 5 surpasses it with its nightstands-gargoyles and smoking skeleton-archers), a reduced number of units, a reduced number of factions, a worse city development system, and a completely new plot instead of continuing the already beloved one. Besides, a sequel should always be better. Heroes 3 was a breakthrough, Heroes 4 was slightly above average. That's why many fans of the Elder Scrolls series don't really like Oblivion; Daggerfall was a breakthrough, Morrowind maintained the brand to some extent, but Oblivion simply became another good RPG.