Warcraft III is instantly a classic of any genre.
As you play the game with the chosen character for that map, you lead your troops through the world (not an open world) to complete the quests given. You can even find side quests here and there as you go. The lords you play level up and gain new spells and abilities as they go. There are even items you can pick up and use. The missions are challenging, some more than others, and are enough to keep you on your toes.
The world is beautiful. It's done in the classic Blizzard, cartoonish style, but it's vibrant and alive. There are plenty of areas off the beaten path to explore, too.
The gameplay isn't over tough, but it will challenge you enough to keep you interested. All-in-all, this game is a classic and one of the best games around.