Tropico 4:
Probably the best Tropico game that exists. Tropico 1 is the game that started it all, way back when, and although it's still a great game it feels dated and clunky. Tropico 2 was an honest effort by PopTop Games to offer a similar game with a distinctly different flavor by placing it in the Age of Sail from the perspective of pirates. After PopTop got eaten by... 2k Games, I think it was, years later Kalypso Games decided to show the world that it had a raging fetish for remaking old games that had a bit of a niche market but had good numbers of dedicated fans that salivated at the thought of playing a remake. Tropico 3 was made, introducing asphalt roads, automobiles, aura benefits for the Presidente, a radio show host that was funny and really set the tone. A lot of fans accepted the new game, but there were several vocal detractors saying that all the different changes were a step in the wrong direction. Then Tropico 4 was made, which was criticized as more like Tropico 3.5, with numerous updates but removing some of the things that made it feel so fresh, like the radio host. However, as Tropico 4 is more like Tropico 3.5, that means that it's the best Tropico there is. The UI is done well, the campaign and scenarios are fun, the whole game feels very refined. The DLC add something like a new building, a new Presidente portrait, and a new scenario each. For your money, they're probably worth about $1~$3 each, unless we're going movie-theater-rate in which case something like $5-$7 for the amount of time you'd be playing a given scenario. Modern Times is actually far more like an expansion pack, and IMO it's definitely worth to get.
So that's kind of the history, but what it is is a kind of political, economic, city-building game. Unlike (most) other (traditional) city-building games (Pharaoh, Cleopatra, Caesar series, Zues & Poseidon), there are individual people. These people have their own skills and own personalities (although it doesn't mean much more than where they fall in the political spectrum and what facilities they frequent). Unlike most god games, where you can more or less force people to do what you want, Tropico takes the stance that you must use other forces to encourage people to do what you want, like increased wages at a particular industrial building to encourage people to work there. You also aren't safe in your rule, because if you don't keep the people happy you may find a lot of political opposition come election time, and a lot of foreign opposition if you cheat the elections. If the people become too disgruntled, some may become rebels and hide out in the island jungles, striking at economic and strategic targets to weaken your base of power and overthrow you. It comes down to figuring out how to make money, using the money to invest into your people (or to tighten your oppressive grip and milk them for all they're worth), win over or bribe the populace, protect yourself from rebels and either accomplish whatever you want in a sandbox or complete the campaign. The entire game has a very humorous tone to it, which I often chuckled at. I definitely got my money's worth, and I didn't buy it or the DLC when they were as cheap as they are now.
Sang Froid: I don't even know what that is, sorry.
Magicka: Neat game, but low replayability for me. Beat it on single player. I'm sure the main draw is multiplayer, but I didn't really find anyone that wanted to play with me so I haven't done much with it.
Port Royale 3: Another Kalypso game. I forgot who made Port Royale 2, but Port Royale 2 was a very interesting economic and ship-warfare simulator. Kalypso created a remake of the game, which seemed to stay very true to the original. Unfortunately, PR3 distinctly lacks some of the features that made PR2 so interesting, such as the ability to found your own towns if you got the appropriate okay from one of the naval superpowers. I'm pretty sure you could also take over other towns, but whether you remain in control of them or if you are forced to give control to one of the naval superpowers that gave you a Letter of Marque (sp), I don't remember.
You essentially play the role as a freelancer, and you're able to trade with the four superpowers (England, France, Spain and the Netherlands), build your own economic buildings such as farms and distilleries, get involved in the wars they start periodically with eachother, combat pirates, and engage in piracy. My real issue with the game is that it often feels like automation takes care of everything. Once you get enough money, you buy some ships, create an automated route, and just send them off and as long as you didn't make a really stupid mistake (like giving them no escort and they run into a bunch of pirates) you'll start seeing profit. If naval combat is more your thing, then feel free to do that, but there's not much variety involved.
IMHO, PR3 is kind of bland, good for a decent time investment until you just go "... eh... I wish there was something else to do in this game...". Also, the campaigns are crap. They are not even campaigns. They are glorified extended tutorials, which can be nice, except there's essentially nothing interesting to do story-wise to break up the monotony. There's apparently some DLC that adds campaigns, but I don't know much about it or any of the other DLC.