RPGs have come a long, long way in the last 20 years. You're competing with 5E now, and many more innovative, radical games. I want to share some thoughts I've had in relation to my own designs that you might find useful as you edit and revise.
* One major development in the RPG scene has been acknowledging that there are many, many different play styles. Current expectation is the rules should have a style and POV in mind, the mechanics should support that style of play and the rules doc should be explicit about which target audience and style of play the rules support. I like that you call out that this system is not for high-powered supers campaigns, for instance.
* Another fairly recent expectation is that the rules should give the GM explicit instructions on how to run the game in that particular style. Many things you and I would assume 'a good GM just knows to do this' are now written down as hard-and-fast rules. The goal is to let a group of people who have never played an RPG before follow your rules and not only have a good time but actually reproduce the experience you the designer have in your own play group. It's a very high bar, but even if you get 60% there your game will be much better for it.
* One piece of advice struck me so hard I've made it my golden rule for design: never, ever lose sight of what the people around the table are actually doing, right here in this moment. Are they writing things down with a pencil? Browsing a wiki? Rolling dice? Why, and why just now? Did the rules tell them to do it? Does it support my goals as the designer?
* Related: when you get down to it an RPG is just having a conversation with your friends. The rules drive and guide the conversation, and the point of the whole exercise is to get your friends to say really, really cool things.
You have a strong POV in the rules: "the Adventure System is a game driven by the story and action." A quick skim shows over 100 of your 144 rules pages are dedicated to combat and stats to be used in combat, so that looks to be the core of the game and there's nothing wrong with that. Most of your time in play is probably spent either in combat, setting up combat, or in a scene that provides justification or context for the next big fight. If you spend a lot of time and effort on character arcs and making weighty moral decisions, there isn't much in the rules now to tell a newbie how to do that or mechanics to support that kind of play. Again, nothing wrong with being action-centered, just be sure the rules say what they do and do what they say.
Assuming the game is action/combat centered, I'm expecting the answer to 'what are people doing?' will usually be something like 'I'm listening to the action unfold and planning what I'll do when it's my turn.' So you need to be very sure that the rules drive the conversation to create exciting action sequences (verbally) and be sure the players have important, tactical choices to make on their turn. Those choices should have an immediate impact on the PC, the state of the fight and have lasting consequences in the fiction going forward. (Else why are we fighting?) I haven't read far enough yet to give you specific feedback on this, but that's what I'll be looking for.
