The book opens by trying to explain just what it is. Whilst it wasn't the first attempt at a generic ruleset, most people were publishing discrete games that included both rules and setting (or at least, genre) or they'd gone whole hog at the generic concept, put out some rules and left you to it. Amazing Engine was designed from the outset as a two-part system. You'd have the core rules (this book) and then you'd add the 'universe book' of your choice to make a complete game. These core rules contain all that's needed to create player characters and have those characters use skills, fight, and move. Hence, any character can be played in any universe, and experience from one can be applied to another.
The concepts of a 'player core' and a 'player character' are introduced to facilitate this. The idea is that this System Guide is used to create the player core, which is the framework from which player characters are built. The same player core is used from universe to universe. The player character is the actual collection of numbers, skills, and other abilities used to roleplay in a given universe. A player will have a different character in each universe, but these characters may all be generated from the same player core. It doesn't however mean that they're all the same character, just they share the core framework. That's fine if you like playing, say, sneaky and intelligent characters whatever sort of game you are playing... but may be a bit problematic if you prefer to fine-tune even the underlying nature of your character to the setting in which he will exist.
In the player core, you have to decide how much emphasis you want to put on four core aspects: physique, intellect, spirit and influence. Just how these are expressed will depend on the universe in which you will be playing. This is done by having two attributes associated with each aspect, and it is these, not the aspects, that are used to describe the player character - and can be quite different for each universe. You start by ranking the core aspects from 1 (the strongest) to 4 (the weakest). Then you begin in on your first player character by picking any four of the attributes - it doesn't matter which aspect they relate to at this point - and roll 4d10 and add them together to get a number. For the other four, roll 3d10. Then you add together the numbers for the two attributes belonging to each aspect - this becomes part of the player core and is used to create each subsequent player character (who are made slightly differently from the first one). It sounds a bit complex but the examples given and just getting some dice and playing around make it all come clear. As is often the case, rules really ought to be written by someone other than the person who created them - they understand how they work already and don't always explain them as well as someone who has had to learn them can!
Many other choices have to wait until you have decided on a universe in which to play. You cannot be an elf in a universe that doesn't have them, after all, nor can you wield magic unless you are in one where it works. Although your skills, too, will have to wait until you know about the universe you'll be playing in, the way tasks are resolved when you use them is standard, and is covered here - along with general notes on how they are chosen and so on. It's a slightly odd feeling trying to understand this in abstract, but again the examples are clear.
The next part of the book looks at experience: how to gain it (or award it if you're the GM) and what to do with it. This is when things get interesting - your player character's experience, gained in one universe, may be applied to your player core (and so benefit every player character you have across all the universes you play in... even though they are different people) or you may apply it to the player character who earned it. You also have the option of using them immediately to boost some ability temporarily as the situation dictates.
Other topics such as movement and the all-important combat are also covered here, again in fairly general terms. Whatever you are fighting with, the basics of how to resolve a hit are going to be the same, and the general overview of how combat works is constant. Finally, there's a note on magic, psionics and special powers. Mostly, it says that they are left to the universe books, which will determine what is possible there.
This isn't a game for shifting genres with the same character, yet it allows for some measure of continuity. That's particularly nice if you don't like starting from scratch every time you begin a new game in a different setting, or if you lose a character during play. More than that, it's a bit difficult to say - this is very much half of a game, I'll need to read a universe book to see how the whole hangs together... but that's a matter for another lunchtime! For now, this shows some promise.