Hail to the best Turn-Based Strategy ever developed.
In this game there is a mix of RPG and strategy elements. If you play the campaign, which I recommend to, you'll gradually learn how things work in the world of Erathia. Generally the idea is simple, but there are a lot of tricks that you must figure out by yourself, and don't expect the game's tutorial to teach them. Like in Chess, your tactical decisions may be very subtle sometimes, but they're the key to the victory.
In Heroes III you play with characters known as heroes. They're the only way to move your army throughout the map. Your troops are recruited in the castles, which produces, at the end of an week (or seven turns/days), new soldiers to your army. Plus the castles are responsible for the production of resources (gold, wood, ore, sulfur, gem, crystal and mercury), all of them necessary to build the fair selection of available structures.
Each race has their own type of heroes, soldiers and castles. You can choose between: Castle (humans), Rampart (elfs), Tower (magicians, golems, titans etc), Necropolis (undead), Fortress (lizard-folk), Stronghold (orcs/goblins), Inferno (devils) and Dungeon (manticore, dragons, harpy etc). There is a good variety when comparing the units and structures from each race, and 3DO definitely didn't want to create a template unit and just put a different skin for each castle. They're all pretty different, although the developers were effective to give a coherent balance between the troops from the various races.
You must manage your kingdom in order to protect all your castles and guarantee the production of new units and resources. Then you'll be able to attack your opponent and defend yourself at the same time. This is the basic strategic idea in the world map. To effectively achieve that, however, you must travel with your hero to find important items and special locations, otherwise your adversary will certainly beat you in no time. The artifacts play an important role, since they'll either empower your units in combat or give a nice bonus to your hero. And the special locations are eventually necessary to give a boost to your resource productions, which will speed things up when recruiting expensive units and building your castle.
When you engage in a combat, a hex-grided battlefield is generated in accordance with the scenario where your hero was located; for example, if your hero was between trees, the battlefield will look like a forest. Then, your army and the enemy troops appears. Starts the player that have the fastest unit (this is, the unit that move more hexes per turn). Here, there are some of aspects to consider: flying units, used to pass through obstacles or walls; ranged units; ballistas; catapults, placed in combat only if you're invading a castle; spellcasters, including your hero, that can turn the tide of the battle; and some others special units. All of these troops work in coordinated attacks, and there is no way to win a balanced battle against your opponent if you don't explore the qualities of each unit.
The special units have unique abilities, which allow a good variety between the races. Vampires, for example, are level four units that have the abilities to fly, drain life and attack without be retaliated. A unit from another race with the same level, like Mage, from Tower, is a spell-caster that operates at long distances. Dragons, both from Dungeon and Rampart, attacks with a fire breathe that hits one or two units in just one strike. Hydras may hit all adjacent enemies with one attack. We can continue talking about units in Heroes III for hours, although experimentation is the key.
This game also comes with multiplayer support, to play via IPX, over the net or in the same computer. The problem is that you can't see all the things that your ally is doing if you play a remote game, so it will become tedious in just a few hours. If you want to play this in multiplayer, start a game with other players in the same computer. Obviously, if that is the case, you must play a cooperative game; otherwise the competitive mode would be unfair. =)
It's a classic that is a must play for every RTS and RPG fan. This is not only the best game of the series, it's also one of the best titles ever released in the genre.