If you've not played any of the series before, Anno 1404 is fundamentally a game of trade and production, with a little exploration and a soupçon of combat adding a delicate frill to the edges of the sensible economic tablecloth. The player's role is to populate and exploit land, gathering resources and refining them to produce mercantile or military wares, and to stockpile or distribute these end products as they see fit according to need and priority.
Anno 1404 is quite the looker too, with deliciously detailed 3D building models giving a solidity and genial rurality to your settlements, whilst well-animated citizens bustle from place to place. Trees sway in tropical breezes, sea birds wheel overhead, crops sprout and are harvested. It's soothing, pleasant and absorbing. I'll be surprised if a better-looking RTS comes along this year.
The sense of being totally in control without having to concern yourself overly with the minutiae of day-to-day management is one of Anno's real strengths - once things are set up, they generally continue to work pretty well without supervision. Handy alerts will pop up to let you know when a warehouse is full or a well has dried up, but on the whole the game's pacing allows you to focus your attentions on what you're actually trying to achieve, without all the plate-spinning of many similar titles.