One finger more than the scroll gesture … I’m not sure how you could do it differently. Requiring three fingers on the mouse would just be weird (I’m all for allowing three fingers additionally to two fingers, though!) and requiring just two on the trackpad is kinda not possible (scrolling is obviously more important and scrolling with two fingers is obviously superior to every other implementation of that on a trackpad).
And it’s literally only the number of fingers that’s different. And the only non-obvious gesture is probably to swipe up to invoke Mission Control.
Also, the way OS X is set up, those gestures serve as shortcuts (like hot corners used to, in the olden days). Nearly every single functionality can be reached via just clicking (Notification Center, switching from desktop to desktop or fullscreen app to fullscreen app) or buttons on the keyboard (Mission Control, Launch Pad).
Just relatively less important and central functionality is relegated to either the context menu (the ability to look up words in a pop-over can be activated via the context menu or three finger tap) or keyboard shortcut and gesture (swiping down for App Exposé).
Accepting an arbitrary number of fingers … sure I’m all for it. But those gestures aren’t really anything worth criticising. They are shortcuts that have to be explicitly learned. That’s why there are videos in the control pane. Apple knows that those have to be actually taught. That’s why the UI has non-gesture alternatives that are obvious and in your face.
This is not to defend Apple – I just want to point out that little personal pet peeves like these aren’t necessarily indicative of actual problems actual users have, especially if they come from an expert. (I also think you can always improve things and that’s certainly also true of how OS X implements gestures. But that’s just a truism that will never be wrong. As someone working in the field: Luckily. There are probably juicier targets than gestures in OS X, though.)