Well, I'd argue that the first chapter of KQ9 is a fairly meaty experience. There are up to 52 items (maybe more) to get, and up to up to 48 or so you can get in a single play through (now at least 4-6 of that total items could be counted as minor, as they only influence the story a little, but don't get used in important puzzles, but still get a 'puzzle ding' for doing it/collecting them). I wouldn't quite call them collectables though as you will still use them or lose them in the course of the game's story. There is one exception that does become a collectable, and one item you won't see if you take a certain paths.
If only counting the item puzzles alone, the game is roughly the same size as KQ1-5, which all had about 30-40 item puzzles each. KQ1 only has about 22-23 puzzles in a complete playthrough (optimum solutions, depending on version), and Wizard and the Princess about 22 puzzles.
This isn't getting into other puzzle types tile/jumping/board-game like puzzles (a type of puzzle introduced in KQ6, at least 3 versions, one being in the middle of a chase scene), the quick-time events (weakest type of puzzle), some action oriented puzzles, and conversation puzzle types, and action 'choice' puzzles (to do something or not to do something, or choose between three choices)..
Minor spoilers to follow...
Once you figure in replayability there are at least three paths to take, and these do offer some interesting plot twists at points, .it becomes a pretty chunky first chapter. Now, as for a story, its not the most 'epic' in scope. It's no 'Graham saves the world' kind of thing. It's more or less Graham's trial to become the 'best knight', so he can become 'king'. That is basically the role of the tournament, and why most of the characters have entered it as well (that whoever is chosen as the knight In that tournament will likely become the next king). Because Graham becomes the winning knight, it apparently does improve things in Daventry for a time. But ya with replayability it almost reaches the scope of KQ6.
But 'scope and depth' are relative. I'd say its scope and depth exceeds that of say KQ1 and 2, and possibly 3 (which had fairly bright and whimsical atmosphere considering the topics it covered), but no where near the depth of KQ4 or KQ5 story wise.
But ya, its a rather large game, for a first chapter. It's nothing like the chapters of KQ7, as it mostly stands alone as a story.
then I will happily chow down on my nasty sweaty hat.
Lambonius might have to eat his hat on this one... At least for the first chapter. No telling how long or short later chapters will be.