You take the role of El Presidente, a dictator that calls all the shots and makes everything on the island happen. It's up to you to either make your people happy or build a large enough army to deal with those rebels! As El Presidente, you are offered tasks from the United States, Great Britain, USSR, China and the Middle East to build up foreign relations that can help you in the game. You are also offered the choice to complete national agendas to make your people happier.
If you liked the Sim City series, you'd definitely be interested in this game. The game is full of humour that will have you laughing if not smiling throughout the mission, especially with Penultimo there by your side. I have heard from others than have played the previous game (Tropico 3) that Tropico 4 is very similar and little has changed. I can't really say anything since this is the first game in the series that I have played and have enjoyed it just as it is.
This game can be very addictive and can eat away your days and nights, making you want to finish it. I do recommend you spread the game out though, as I felt that once I completed the campaign, there really wasn't much else to do. There is a sandbox mode and "god mode" so that you could play your own custom made games, but I just felt they weren't really fun as they weren't exactly goal oriented. The game is very long, so as long as you spread it out (just a bit), then this game can last a very long time. Downloadable content has been released recently, giving you extra missions and content and I'm sure there will be future DLC yet to be released!
This really is a game you should try out. At least try the demo that's available for download on Xbox Live if you're still not confident!