All of Part 3 already filmed, Parts 4 and 5 already written...no scrambling to figure out how to end the series at the last minute, this will be an amazing thing to behold (for one reason or another) when all is said and done.
It's very rare to have a franchise of this caliber not adapted from another literary source (whether it be novels or comics) that doesn't adopt the "making it up as we go" approach.