It has always provided variety, detail without being boring, and maintained a very loyal fan base throughout its existence. The graphics are crisp, clear, and gorgeous. The maps are very attractive, and it's easy to determine exactly what everything is. There are a ton of new buildings and objects strewn across the landscape, and they are all quite distinctive. Animation is excellent for all of the unit types.
Music is also very good - it creates a nice background without getting in the way.
For those not familiar with the series, gameplay is turn-based. You have a certain amount of movement available to your heroes. This is used to explore the land, searching out your goals. When combat begins, it too is taken in turns, with the fastest unit moving first. You may take your time to evaluate a situation and act accordingly.