+15 Villager HitPoints
+50% Siege Workshop Unit's Fire Rate
+100% Farm Production
Sumerian is extremely similar to Hittite. Both civilization get the same superunits and they also have advantaged catapults. However, Hittite gets Armored Elephants and better technologies, Sumerian doesn't. Sumerian has double firing catapults which makes them able to beat any other civilization's catapults except for Hittite. For that reason, Sumerian is only effective when there is no Hittite player opposing you.
The faster firing catapults are both a blessing and a problem. Bunched catapults still get nailed even by regular Heavy Catapults. And while opposing catapults can still hurt Sumerian catapults, the faster fire also is able to kill on coming units better and can burn building to the ground faster. If any unit penetrates past the catapults, Sumerian will slaughter itself to death.
The same problems that Hittite has, Sumerian shares. They swallow down wood excessively and they can be nailed from infantry and stable units. Sumerian differs from Hittite in a few areas. Sumerian has worse technology than Hittite. Most notably, the lack of coinage, making tribute a waste. Sumerian makes up for it by having Long Swordsmen as well.
Good Hittite players who play a siege role with no opposing Hittite player, may consider Sumerian over Hittite. They demolish towers faster and can kill legions easier. Basically, however, the two tribes parallel each other.
Frozen_DashDog's Run Down
SuperUnits: Ballista Towers, Heavy Horse Archers, Centurions, Heavy Catapults
How To Play:
I would play Hittite over them. The lack of Armored Elephants cripples them. If you do get stuck with them, however, make sure that you play them almost exactly like Hittite, just don't build Armored Elephants. They're good and all, but why get a watered down version of Hittite?