Tropico 4 is the follow-up to Tropico 3 (released in 2009) and Tropico 3: Absolute Power (released in 2010). All three games were developed by Haemimont Games, which is notable because the franchise had previously played a lot of musical chairs with its developers. Unfortunately, Haemimont Games hasn't shown a lot of creative spark. Tropico 3 was basically a re-make of the original Tropico, and now Tropico 4 feels more like a second expansion pack to Tropico 3 than a full-fledged sequel.
In the Tropico games, you take on the role of El Presidente, and it's your goal to run a Caribbean island while simultaneously keeping your people happy and squirreling away some money for yourself. For the most part, these objectives are met by you ordering buildings to be constructed on your island. You might build a pub and a casino to keep your people happy, some farms to generate exports for a profit, and a bank to siphon off some of the proceeds for your Swiss bank account. Tropico 4 includes over 100 buildings, so you're given lots of options for how to run your island.
Tropico 4 adds a few new things to the franchise. You can now import as well as export products (and some products, like uranium, can only be imported). You now have to hire ministers before you can issue edicts (and since ministers are high school or college educated, that means you can't issue edicts right away). Europe, China, and the Middle East are now included as minor foreign powers, and you have to keep them happy along with the United States and the U.S.S.R. There are now many more natural disasters to worry about, including volcano eruptions and tornadoes, but you're given a convenient rebuild button to make your recovery easier. And Tropico 4 now links to Twitter and Facebook, if that sort of thing interests you.
Some parts of the game have been overhauled as well. The graphics engine looks identical, but I found that the game ran much more smoothly than before. The radio broadcasts, which were sort of grating and annoying in Tropico 3, were completely redone, and now they're pleasant and amusing. And the interface saw several tweaks to make the game easier to manage, including a new "tasks" system where your objectives are shown in the main interface, and you don't have to keep opening up your almanac to see how you're doing (now if they'd just add happiness to the main interface as well).
Sadly, though, there isn't much new in the game other than the tweaks listed above. There's a new campaign, which features 20 scenarios, but just like in Tropico 3, the scenarios aren't much different than sandbox mode, and you're usually allowed to play your island any way you want. There are also some new buildings, but they're sort of odd. For example, there's a stock exchange, but it doesn't have anything to do with stocks. Instead, it allows you to rent out businesses, making it more of a realtor's office. Meanwhile, you can add a shopping mall and a museum of modern art, but they're backwards. The shopping mall loses money hand over fist while the museum is quite profitable.
Finally, in perhaps a sign of the times, Tropico 4 is much easier than Tropico 3. I went back and played a little Tropico 3, and I was surprised at how much trouble I had keeping my people happy, at least at the start of the scenarios where the happiness rating kept hovering around 40%. Meanwhile, in Tropico 4 I don't think my happiness rating ever fell below 45% at any time in any of the scenarios, and with happy people you don't have to worry about rebel attacks or coups or protests, or getting voted out of office, and half the challenge of the game disappears.
Tropico 4 is a difficult game to rate. It's a perfectly fine game, it ran smoothly for me, and it kept me reasonably entertained for about 50 hours, but it's also essentially the same game as Tropico 3... which was essentially the same game as the original Tropico. If you've never played any of those earlier games, and if you like city building, then by all means try out Tropico 4. But if you've played the earlier games, then you might be better off firing up Tropico 3 again rather than plunking down $40-50 for what amounts to a glorified expansion pack.