I have played a lot of RTS games over the years, but I have never enjoyed a game more than the Settlers. It seemed like it was once one of the biggest RTS franchises in existence but it has sort of vanished over the years.
The 10th anniversary for the second game was the last game I really got stuck into and enjoyed. Heritage of Kings was also a really good game. I just liked the aspect of building a wood chopper and a saw mill before you can actually use the timber. Can anyone suggest some other good games like The Settlers that have all the normal RTS aspects of the game play but also go into some detail around resource gathering?
Age of Empires II HD

Age of Empires has to be the first suggestion for games like The Settlers. The gathering of resources is a lot more simple, there are less types of resources to collect and there is no buildings that really depend on another to obtain the resources they need. The gameplay and battles are the same kind of thing in both games. AOE 2 is the best entry in the series, but the first game is in the process of getting a remaster.
Warcraft III: Reign of Chaos

Warcraft actually started out as an RTS and it was a very good one at that. There is a focus on base building, exploration, hero units and there is a good story to wrap it all up into a really good RTS game. The setting is complete fantasy rather than trying to be somewhat realistic like Settlers is, but it really is a good game.