Overlook is a one sided assault map. This is clearly going to be a map that is suited best to a one sided objective game. The map consists of a base that encompasses the entire "back wall" of the map. The map, in the Beta, was only used for Generator Defense, and it is unclear whether or not that gametype will appear in the final game, but Overlook really seems like a map that is built for a specific gametype, like Generator Defense. One team spawns on the offensive side of the map, attacking the base, and the other team spawns on the defensive side of the spawn, inside the base. The map is set on, what seems to be, a farm. The main base building is the only real indoor area of the map. There is sparse cover outside in the form of bails of hay and lean-to buildings on the side of the main base, but for the most part, the building and the building's perimeter are the only real cover for the defensive side of the map.
The offensive spawn is very open, the attackers approach the base from the bottom of a hill, which leads over a small stream, up into the base's compound and the building itself. It is a completely open area, the only cover is large rocks out in the open and a tiny sheltered crossing on the bridge that leads over the small stream in the middle of the map. The attackers are at a natural disadvantage, as the defenders have the high ground and the natural advantage because of it.
For Generator Defense, there are no weapon spawns on the map. The only available weapons come from Weapon Drops that happen periodically throughout the game, or weapons availble through Loadouts. The weapon drops are always good weapons. Rocket Launchers, Sniper Rifles, or Spartan Lasers are among the most common drops. The loadouts available are fairly powerful also. From the get-go, the humans have Shotguns available, and to balance things out, Elites have swords available right from the start.
When the full version comes out, there is sure to be weapon spawns on Overlook for game types other than Generator Defense. Right now though, this is all we have to go on.
It's important to lock down each Generator. There are three to defend at the start of the round, and approaching them and pressing X will lock down the Generator. This means that a heavy metal sheet will come up around the generator, making it harder for the Elites to crack it's shielding so you will have more time to fight them off while they try to break through the Generator's defense to it's vulnerable core.
Don't forget that there is ammunition crates back in the Human base, so don't throw away that heavy weapon you got in a weapon drop just because you're out of ammo. Make sure to go back and get more ammo for it until you die with it, to keep the heavy weapons in circulation for your team for as long as you can.