Alright. This may get a bit long-winded. Tropico as a series is you taking the role of a Dictator in a Banana Republic and maintaining your position by whatever means you see fit, while smuggling a bit for yourself on the side in your Swiss Bank Account(that's actually what it is by name). You could go the total Benevolence route and actually give a fuck about your
communist slave labor citizens, making sure they have all of life's necessities and then some, like actually good schooling, healthcare, and more rations. Or you can go full Dicktator and gun down your political opponents, rig elections, and have everyone starving in bread lines while you give your soldiers free blowjobs so they'll stay loyal and keep gunning down their countrymen that the state police determine to be undesirables. Realistically, you're going to be somewhere in-between.
The entire game takes the format of, as stated by Worg, a City/Nation builder with numerous scenarios and, depending on the game in the series, a (mostly)solid campaign experience, along with the expected free play options. Replayability is pretty high if you like to go back and experiment with what works with your kind of playstyle. Think of it like going back to SimCity and fucking around, watching stuff just exist.
I've not mentioned 6 yet specifically because, frankly, every game excluding 2 has been pretty much the same thing, just with graphics changes and various enhancements to the formula. When 3 came out, it was said to be a 3D remake of the first game, and that's arguably correct. 4 wasn't much different, but added a few really nice things on the side, so it beat 3 out. 5 added some more stuff, including Dynasties which nobody gave a damn about, while also removing some things from 4. Finally getting to 6, it looks like they took the great from 4 and the things anyone gave a damn about from 5, and added some
really nice shit like actually building bridges and shit between islands.
TL;DR Played any SimCity that wasn't the shitty new one, and felt like you wanted to get more politics and humor? Maybe have your military gun down political opponents and protesters? Maybe you just like Llamas? Get the game and enjoy
absolute power, now with bridges and landmark theft, and probably all the crap that was DLC in 5, like creameries.