So just like the Battle of the Blackwater, the fortress has a lightly guarded wooden door at ground level with only a few guards where attackers can easily kick it in. No moat, not even a proper bar on the door.
I was saying before the episode that if my castle had something like The Mud Gate, I'd have 100 tons of cut stone blocks handy to barricade the damn thing.
Like the cast of the unwatchable "Falling Skies," these guys don't train, they just yell at each other.
Also, if the Watch is spread so thin that it can only defend a small portion of the wall, why does Nance attack at the only place there are defenders? Does the tunnel got through the wall? That kind of negates the whole purpose of a wall.
And of course previously we saw Bran use a secret tunnel that comes up through a well in the fort. Is that the same fort or a different post?
Why do they wait for the mammoth to be hitched to the gate before they dump burning pitch on it? I bet a mammoth would pull twice as hard when its ass is on fire.