There are two ways to play this game. You can play it properly and advance through the game, battling enemy nations as you go, in your ongoing conquest to... well, I dunno, I never got that far. Because I played it the other way: I just built stuff and watched the Settlers mill about for the first few stages. It's like a precursor to The Sims, except if you actually progress, there's battles and sieges instead of tickle fights.
This game is considered by far and wide to be the definitive entry in the franchise. There was even a 10th Anniversary remake made not altogether long ago, which sadly saw a very limited release. (It's pretty awesome too.) Having tried the others briefly, this is the one I keep coming back to -- despite my insistence on doing nothing but building.
For speed demon strategy gamers this game may be a bit disconcerting; no matter how well you know the terrain and how quickly you're able to dispatch orders, your Settlers can only do their tasks so fast. They have a very casual attitude towards everything. But if you enjoy watching little sprites run around -- in a beautifully animated little world -- cutting trees and prospecting for gold as you lay out your plans for conquest, you'll find yourself right at home.