A word of warning first: If you're not willing to spend at least a couple of frustrating weeks learning the very basics of a game before you can survive the first few turns, this game isn't for you. No Greater Glory is one of the last truly 'expert' wargames - a genre very popular in the 1980s. If you give it time to grow on you, chances are you'll grow to love it.
On the surface, things aren't that bad. The game takes place in the United States where civil war has just broken out. It is controlled by fairly intuitively structured screens providing clear information and listing the available options. This makes it attractive to 'just try things out' carelessly. Which the game punishes almost immediately, though. Even on the lowest of the five difficulty levels (mislabelled 'very easy'), the computer-controlled side will gain the upper hand against any casual player right away.
The problem also isn't that an unmanagable amount of options is presented to the player. The game is structured in clearly defined phases (movement, attacking/defense, domestic politics, foreign politics,...) with only a few decisions being demanded from the player in each. It's the subtlety of many of these decisions which makes it so hard.
The very first decision of the player is to appoint a cabinet, for example. Here, the player has to take various factors into account; among them are the loyalty, the ability, the party membership and the state of origin of the candidates. If you appoint only people from one party, the other one will be pissed. If you don't appoint people from a certain region of your country, states in that region will be less sympathetic to your cause. Weighing these factors isn't easy although the game gives a decent amount of feedback concerning the effects of your decisions.
Same with the foreign policies. Depending on whom you play, you will want to get the European powers England and France involved or to stay out of the conflict. How do you achieve this? By threatening to cut off delivery of raw materials? Or by being nice? And whom do you send as ambassador?
Even the war itself, as straightforward as it may seem, is influence by such factors. Moving armies around is easy enough (provided you don't get into problems with recruitment, infrastructure or logistics - did I already mention this is a very complex game?), but whom do you trust with command of which army? How do you keep the soldiers morale up? How do you counter the effects of the other side's propaganda efforts?
No Greater Glory is absolutely excellent, save for one thing: the difficulty. Not the fact that it's difficult per se, but part of how that is achieved. The AI cheats [see below for Ed Bever's comment concerning this]. No matter which side you choose, you will always have severe internal problems to overcome in the early game: the congress won't let you increase taxes or introduce conscription, preventing you from earning enough money and building up a decently sized army - while your opponent apparantely doesn't have those problems at all. There are nasty indirect effect of this, too. So you can't recruit a big army; which means that your generals will be disappointed with the commands they receive; which means that their home states will be disappointed with you for not fulfilling the wishes of their local heroes; which means that in the best case, you will only be able to recruit a few less soldiers next round, but probably, it'll even cause riots against your government. Again, no problem on the other side of the war - unless you take control of it yourself in the next game.
This cheating is unfortunately all too obvious. Most importantly, it's completely unnecessary. The AI opponent plays just fine. It would be still a huge challenge to beat it on fair terms. If you can look beyond that, you'll find an extraordinary multi-faceted strategy game which will keep you occupied for years to come.