Standalone scenarios have customizable difficulty levels so everyone can be challenged as much or as little as they like. Overall I found the difficulty level of the campaign scenarios on the low side, but I'm a veteran of the system, so it may be tougher for others. When a hero leads his army against another hero or town combat ensues. This can be resolved by the computer automatically, or you can fight the battle using the tactical combat engine. This puts you on a hexagonal grid with your troops arrayed on one side and the enemy on the other.
Units take turns moving based on their speed.
Each unit can move and then attack any adjacent units. Each unit can also defend, essentially attack a unit that just attacked it, each turn. Ranged units can attack any unit on the field, but closer units take more damage. Your heroes also improve the attack and defense ratings of your troops and can cast magical spells to help your units or hinder the opposition. Tactical combat is quite fun, each battle takes at most a couple of minutes and the winning hero gains experience based upon the values of the units killed.