This, we're led to believe, is the end: the final set of downloadable maps for Halo 3. Despite the game's continuing success on Xbox Live, Bungie reckons there's enough meat on those multiplayer bones to keep us all going. So, with the possible exception of some new stuff (unconfirmed, as yet) in Halo 3: ODST later this year, the Mythic Map Pack is the swansong for Halo 3 multiplayer.
Of course, that doesn't mean that the end is nigh for Halo 3 itself, whose player population remains robust (even at off-peak times, I was able to fill up games on the Mythic maps almost instantly). And it's not even the end of "new" content, in a sense, because player-created Forge maps will continue to appear for many months if not years. In fact, one third of the Mythic Map Pack is aimed at encouraging Forge. Sandbox is a smaller version of the gigantic desert map Sandtrap, and it boasts pretty much the most customisable Forge layout we've seen so far.
Every ramp, surface and structure in the map is a Forge object, which means that creators can wipe the slate completely clean and build a new level as they see fit. Although the default layout is played out entirely at ground level (albeit with plenty of fortifications, ramps and so on, creating a two-base layout that's ideal for CTF-type games), there's also a basement and a sky level for creators to mess about with if they need a bit more verticality.