Overhang is great map because it blends close quarters combat with long range battle rifle fights. There are two maulers (one on each side), a sword in bottom middle, an overshield in the middle-middle, and rockets in top middle. In the beginning most people go for the center to gain the power weapons and it gets the game off to a fast start. Good teams will need to balance who goes to the top with who goes to the bottom. They will also need to be careful not to just rush in lest they get killed by grenade-spamming opponents. Overhang works well with both battle rifle starts and assault rifle starts. I prefer battle rifle but thats just me. The towers and bases are set up to allow for intense close quarters combat where a well timed jump or melee could make all the difference. There are excellent lines of sight from the upper level although good teams can efficiently use the lower level as well. You can get from one side of the map to the other fairly quickly but not too quickly. I have had no problems with spawning. Overhang is symmetrical. It's best for 4v4 Slayer, Multi-Flag, Oddball, and KoTH. There are 4 BRs, 2 Carbines, 2 SMGs, 2 Maulers, 2 Needlers 1 Sword, 1 Rocket Launcher (I put this in instead of sniper because sniping was really "unfun" on this map), 8 Frag Granades, 4 Plasma Granades, 1 Overshield, 1 Regenerator, 1 Bubble Shield.

Screenshots:

Blue Base

Red Base

Red Tower

Red Sidewalk

Red Tower view 2

Blue Tower

Blue Sidewalk

Center

Top Mid

Mid

Bottom Mid

Blue Sidewalk view 2

Overhead

Here are some gameplay films:
Bungie.net : Halo 3 File Details - Team BRs
Bungie.net : Halo 3 File Details - Multi Flag
Bungie.net : Halo 3 File Details - Team King

Here's a link to the Bungie submission where you can download it:
Bungie.net : Atlas : Private Forum : Overhang (sandbox crypt variant) - Overhang