What I find most amazing about these engines isn't the complexity but rather that they operated successfully despite multiple errors. We are often told that a single failure will destroy the craft, but that really wasn't the case. Shuttle make it to orbit with multiple cracked tubes in one engine. Some bits from the recovered F-1s show clear manufacturing errors. Building something that will work at these energy levels is hard, but creating something that can survive multiple random failures and still keep ticking is spectacular.