Supreme Ruler, like Making History or Europa Universalis, is an extraordinarily detailed and complex grand strategic game covering the entire globe, with economic, military, and diplomatic aspects. As long-time readers may know, I'm a sucker for this kind of game.
Unlike the others, Supreme Ruler is set in the modern world -- sort of. It's set in a hypothetical near future, which is canny of BattleGoat but also somewhat disappointing; canny, because if you try to simulate the real world, you're always going to get flack on minute levels of detail (e.g., "I am from the country of Mystflx, but why don't you show the iron mines at Qwertyuiop?"), so it's easier to create a game that is representative, but not an explicit simulation. Disappointing, because playing around with a good version of the real world would be interesting.
Like other games of this type, Supreme Ruler has a very steep learning curve; expect to screw up royally the first few times you play, and to start to feel a sense of mastery only after you've invested a dozen hours or more. Though the game contains what it calls a "tutorial," it's little more than an introduction to the UI; and the demo does not, alas, contain a version of the manual (which is, in my opinion, a bad choice on the developer's part -- getting into a game like this is hard enough, and the demo would be a more effective sales tool with better newbie support). Luckily, there is a Wiki for players, containing a "Total Beginner Guide" which is actually a good starting point.
The full game contains three "campaigns" (actually, sandboxes). The main, and most interesting one, is set in a world reminiscent of Ron Goulart's old science fiction novel, After Things Fell Apart -- all the world's countries have fallen apart into tiny little polities, from, say, the Commonwealth of Massachusetts to the Kingdom of Naples, but from time to time, a region may vote on "reunification" -- and if you, of all the ministates in the area are doing best, the region may reunify under your command. Another has the same background, but cranks up the crankiness level, if you will -- so that AIs wage war, with each other and with you, at the drop of a hat: a version of the game for those who want to concentrate on the military aspects. And the final version has the world divided into more or less its current array of nation-states.
In addition to this, there are scads of scenarios -- of which three are included in the demo (none of the campaigns, or multiplayer play, are in the demo). One starts with Northern and Southern California at war with each other; one allows you to play as any of the four Italian ministates, working toward winning an upcoming reunification election; and the third depicts an Israeli/Syrian war.
Supreme Ruler contains all the elements you expect in a game of this sort -- more than a dozen different resource types, expanding production, the ability to micromanage social spending, trade, diplomatic relations, technological advancement, and a large number of unit types. In fact, the variety and level of detail is initially overwhelming, mitigated somewhat by the fact that your cabinet can make decisions in any areas you don't want to concentrate on personally (though hiring the right cabinet members then becomes important).
When I began playing Supreme Ruler, my expectation was that I would like it less than other grand strategic games because of its near-future setting; the connection to history is, for me, one of the main appeals of games like Making History or Crusader Kings -- even if I'm pushing for an ahistorical outcome (the survival of Byzantium, or Argentina's conquest of South America), there's still the feeling that I'm doing it within some well-defined historical parameters. Supreme Ruler feels more "game-y," that is, less tied to reality; and yet I discovered it had another appeal I hadn't quite expected, which is, in essence, rooting for the home team. Playing as Ohio, you start to care about the Buckeye State, and there's a certain glee in smashing those jerks in Indiana. Realistic? Not so much, but entertaining.
With most strategic-level games, the explicit objective is world conquest; what I find most appealing about grand strategy games is that while they permit this, they don't make it easy. It's not simply a matter, as in Risk, say, of building the largest army; you also have to reckon with your economy, the support of your population, and the reactions of other powers. In other words, games of this type place major obstacles in your path, if world conquest is your goal -- and interesting obstacles, or problems to solve, are in fact the key thing about making any game interesting.
And, conversely, they allow for alternative styles of play, as well; while Supreme Ruler doesn't have anything like Civ IV's cultural victory, you can certainly choose to concentrate on economics, your population's well being, and diplomacy, working toward winning reunification votes and the like. You probably won't be able to avoid military conflict entirely -- some bastard will attack you at some point -- but you can certainly avoid being a warmonger. And that's interesting, too.
In general, Supreme Ruler is of a class of games I admire greatly; and surprised me as more interesting than I had expected. It also seems to be better balanced that many grand strategic games are when they launch (it's often best to wait for the first few updates for play-balancing purposes) -- perhaps that's because it's a sequel, and the basic kinks have already been worked out of play.
Because of its length, complexity, and steep learning curve, it will obviously not appeal to everyone; but if you do like this style of game, it's well worth checking out.
(And if you'd like an introduction to the genre, I'd heartily recommend Europa Universalis II, which is rather simpler, and currently on sale for a mere $15. There is a III, but II is simpler, and therefore a better introduction anyway.)