One of the best products from the best strategy games creators from the '90s, it's still one of the best games ever.
My following statement is a matter open to debate, but I think that the peak of their OWN programming efforts is Master of Orion 2 (I put aside their still incredible X-COM because it was not developed by Microprose itself but by an English team called Mythos). Notice that I don't mention Civilization at all. The reasons for that will be stated next.
Master of Orion 2 belongs to a category of games that may be denominated "Civilization in deep space". It surely has a big influence from Civilization, as you can see from what's all about: you command a certain species and your aim is to explore the universe, expand, gather resources, do research, conduct successful diplomatic relationships with other races, go to war, make peace, give bread and circus to your people, and some day become the Master of the Universe in spite of He-Man. This idea is one of the most revisited and cloned of the whole industry, and perhaps even more than Civilization itself (you can read the whole history of this kind of games in GameSpot's History of Space Empire Games feature, which could be found on the MOO2 summary tag). Let's mention a few examples: Space Empires IV and the really successful shareware game VGA Planets are members of the same family as Master of Orion 2. Not every kin was successful; as a matter of fact, only a few of them were good games indeed. Master of Orion 2 was, by far, the best of them all; and it deserves this appreciation thanks to its outstanding features.
One of them is the high rate of customization of the game. Every time you begin a game you are prompted to choose an overall difficulty level, the size of the galaxy, the richness of the planets on organic or mineral deposits, the total number of races in the game, the starting technology level, and the presence or not of random events. Each of these decisions may increase or lessen the complexity of your game. If that wasn't much already, you can choose to create a brand new race and play your game with that one instead of the built-in races. As you can see, these possibilities of customization ensure a very high rate of replayability.
The other outstanding features of MOO2 that makes it such a perfect game are better understood if we compare them to the correlative ones from Civilization. I will make a short list, so you can see in which way MOO2 surpasses its predecessor and model.
For example, the research tree. In Civilization, the research tree is very simple, being composed of single subjects that must be studied one at a time; so you'll always manage to investigate the whole research tree some way or the other: the only challenge is to do it fast. In Master of Orion 2, that's not true. Each area of study is twofold, threefold, divided on four; and unless your race has the Creative perk (which allows you to research everything), you'll only acquire one or two subjects with every research. And yes, fast still is better. It's not strange, therefore, that the Psilons race were intended for beginner players. This leads us to two conclusions: one, you won't always discover every technology of the game; and two, you must be in excellent diplomatic relationships with every race so you can keep asking for knowledge exchanges (and checking if your neighbor is not building a Doom Star by the way).
Which leads us to another outstanding MOO2 feature: the diplomatic feature. It's true that the diplomatic system of MOO2 is almost equal in design and outline to the one from Civilization, but there's a big difference between them: the level of realism. Diplomacy is not a strong issue of Civilization, and even if you're pointing towards the Alpha Centauri ending you can finish the game without ever contacting another nation's ambassador (unless they contact you, of course). And when you do use diplomacy, it turns out that it's almost pathetic, since you can manipulate and betray AI players as if they were babies. Signing a peace treaty with your AI neighbor just to make it easier to conquer him the next turn is still one of the main strategies of Civilization. On the other hand, I have noticed that in MOO2, diplomatic betrayals, treasons and backstabbings tend to have deeper, more logical consequences than in Civilization, even if you're playing it in the Tutor difficulty level. And, as I have stated earlier, diplomacy becomes a strong issue of the gameplay thanks to the limited research. The diplomacy system was already great in MOO, but in this sequel it's even more complex.
Another interesting feature of MOO2 is the possibility of constantly upgrading and customizing the ships of your fleet with the technology you have at hand. Likewise, the addition of leaders, which can be sent to command your colonies or ships to gain bonuses to your production or your military performance, was also a great idea indeed.
But perhaps the most cool (and, paradoxically, the most shocking) thing about MOO2 is that it manages to be hugely deep, complex, and addictive while being basically menu-driven. You won't see units moving around your screen and talking to you. You'll only see colorful speechless dots, and a menu, and lots of text; and the only thing you'll do is to give orders to the program, just as if you were driving a simulator. The only exceptions to this are your colony screen (where you can get a beautifully rendered panoramic view of the planet and the buildings of your colony), your laboratory screen (somewhat commonplace, but effective), and the embassy screen (absolutely impressive, with a perfect simulation of a holographic projector that sometimes gets static and interference on the projection, and excellent musical leitmotivs to each race that otherwise are inaccessible). This is where MOO succeeds while its other family members fail: their designers have made a lot of hard work to bring a blood-warm life to an interface that other similar products from other companies made even more insipid and boring than normal; and they must be praised forever for creating with such a effort of craftsmanship such a rich and complex game. As another player review says, MOO2 still has no other game that compares to it, and he/she is absolutely right.
The only drawback of MOO2 is a direct consequence of its (for me) appealing level of complexity. It has a very steep learning curve. You don't learn to play it just on ten minutes, and without a friend or a printed guide that could teach you how to play it MOO2's mechanics could get hard to grab. As a matter of fact, MOO2 is perhaps the only game of the whole industry, besides flight simulators, whose documentation material is completely fundamental in order to play. Therefore, impatient gamers who prefer to engage only fastfoodish, prêt-à-porter entertainment will get frustrated almost immediately. This doesn't mean, however, that MOO2 is a game intended only to scholars of some kind. It only means that it demands patience and more time for learning it than other games. With this in mind, if you feel that you can tolerate MOO2 steep learning curve, you certainly should add it to your collection. It is, maybe, the ultimate strategy game; and since there are a lot of guides for it on the web it would be a shame if you don't give it at least a try.