The definition of Agile development. They were cut off from making the third act, but the first 2 acts they did make are 100% done, tested, and perfectly functional.
The physics and combat sandbox combined with more modern 3rd person controls are extremely polished and allow for multitudes of choices in everything from mission objectives to even just how you eliminate simple enemies.

Kiefer Sutherland replacing David Hayter resulted in an overly expensive VA for Snake and thus Snake mostly doesn't speak, in a series renowned for monologues and conversations...
Story was tragically unfinished as Kojima was forced to release.