In a short FAQ on its blog, 343 Industries notes that the maps previously exclusive to Halo: Combat Evolved and Halo 2 on PC will in fact be a part of Halo: The Master Chief Collection.
Weapons like the Fuel Rod Gun and Flamethrower are also included, which should be extra fun for folks who only ever bothered to play Halo on a console. It’s certainly been a while.
There’s going to be matchmaking playlists with, among other things, radar enabled and disabled. Also: “All of the game types and custom game type options you remember from Halo: CE will be available in the custom games menu.” What a time sink this collection is going to be.