Age of Wonders is one of my favorite series.
The first one has the best custom hero making. Magic is a huge boon, but it's not really a requirement. The second one switches your hero's focus to magic all day and night and really expands on the magic system. The third one is basically the second one, but better and with one of the best unofficial patches you'll ever see in a game.
If you don't want to play through the entire series, the third one's the one to get. It's pretty awesome.
More detail:
It's a turn based strategy game. You control a hero (Or, in the second and third games, a wizard) who runs around killing other dudes. You choose from a variety of races (Dwarves, Elves, Humans, Halflings, Orcs, Goblins, Undead, Nomads, Cat People, Angel People, Dark Elves, Snow People... The third one adds two races, the Shadow Realm peoples and the Shadow Realm demons. There may be a couple more I can't think off of the top of my head), and train up an army to go kill the other dudes' dudes, and maybe even the other dude. Each race is different enough, though they all have the same number of units available to them. Your regular dudes can gain three levels (Bronze, Silver, Gold), while heroes can earn a bunch of levels. In the main campaign you keep all your heroes and can bring over well trained dudes, too.
Magic plays a huge role in the game. You research spells, find spells, trade spells, and then use them. There's the generic combat spells, the buff spells, the enchantment spells, and the cool overland spells that can do stuff like completely change landscapes. As the undead, you can drop a spell that turns your lands into a waste so you can get a bonus to your income. Because you're undead.
The game has two layers: Overland and Combat. In the overland you manage your cities, tell your troops to go places, research, and all that jazz. In Combat, you attack cities, farms, troops, neutral monsters, and stuff. You can do combat automatically, but you generally lose a few dudes if you do that.
The best part of the series is, without a doubt, the level editor. If you like sitting down and creating a fantasy world with humongous caverns and armies and epic battles, AoW is worth it just for that. The map editor is truly fantastic, and it's really easy to use.
It's a great game. The third one, Shadow Magic, is one of my all-time favorite games ever. The first one is probably truer to the Lord of the Rings feel the game was going for, but after that it went its own direction, and it worked out very well.