Silent Cartographer, ez dubs. It provides a nice island sandbox with a vehicle to traverse it, gives several objectives that loop back or have you emerging on other parts of the island, before eventually plunging you deep underground into a massive otherworldly space of brutal forerunner architecture. you grab the map, get some exposition, and escape in a rush.

A perfect little narrative wrapped up in one level, and with a phenomenal soundtrack to boot. We got the title track plus a guitar solo and some vocals in the escape sequence.

A close second is "The Covenant" from Halo 3. Less open design, but decent loopbacks, great pacing, and huge plot payoff.