And there's a noticeable drop in quality. Not to the point that I'd say they aren't worth getting, just noticeable. I'd say they are something like 50% the price for 75% the quality.

And to be more specific, I'm talking about a breadth of quality issues, from piece durability, to how consistent the fit is, to how easy the combination steps are structurally (as in some steps from the knockoffs require figuring out where you need to hold the parts for support or where to apply force to avoid collapsing another part of it as you build it up).

Lego has it down to a science and there's more to it than just the physical shape (which itself is easier said than done and requires a certain level of precision).