The 15-player Battleground has an attack and defend scenario, where the objective is to capture the Titan Relic housed inside a keep at the southern end of the map. It is very similar to Wintergrasp, and is a fast-paced Battleground where players literally race against time. Attackers, split into two groups, arrive on two boats on the Northeast and Northwest portions of the map. When they land on the beach, four siege vehicles are initially available to attackers, who must break down gates to get to their goal.
These siege vehicles are identical to the demolishers found in Wintergrasp, with about 80,000 hp and the same offensive capabilites. Players on foot can pick up Massive Seaforium Charges in Seaforium Barrels throughout the map. These explosives can be placed near gates to deal damage to them. Players on defense, meanwhile, can man cannons that flank each gate. These cannons have 60,000 hp and have very long range.
The problem with Horde always starting first is more a question of efficiency than anything. When teams of equal skill are under the same scenario, a good team on defense will take a full ten minutes to defend while a good team on offense, for example, will take maybe four to five minutes to capture the relic. Now, this means a good Alliance team can conceivably end the game in under ten minutes while a similarly skilled Horde team needs about fifteen to accomplish the same thing.
Another argument goes that in cases where teams haven't filled out when the game begins, the defending team starts at a disadvantage. Essentially, the Alliance have about ten minutes to fill out in a map that favors offense, and by the time the sides switch the Alliance will almost always have a full complement on defense. I'm not so convinced that this is a problem, really, considering that an undermanned team is an undermanned team regardless of whether they're attacking or defending.
That said, Blizzard has promised to fix the single biggest problem with what is the most balanced and just about perfect Battleground ever released. There can be no gripes about map design because players take turns on both sides -- this is still a problem with Alterac Valley's geography. There can be no gripes about time, as it's guaranteed to end in a short 20 minutes -- who can say that about Warsong Gulch? As great as Arathi Basin and Eye of the Storm are, the one thing Strand of the Ancients has over either map is the timer.