Why is everybody so concerned about the AT-AT scene? It makes perfect sense, the speeder hits the unarmored neck and destroys it. It's not like such things don't happen in tank vs tank battles, for example.

The armor of the Soviet KV-2 tank was too thick for the standart German anti-tank guns of 1941 (47mm and 57mm) but a successful hit in the turret ring could disable it and effectively destroy the tank. I remember reading about a lone KV-2 that held off two battalions on a bridge until expert gunners blasted of the cannon and then put a shell through the thin ring between the turret and the hull.

Same wit the AT-AT, the fact that "the armor is too strong for blasters"doesn't mean it doesn't have weak spots or that it is uniformly thick everywhere. The neck, for example, was never fully armored - check the "Incredible Cross-Sections" books.

I think it's an interesting idea to have the side door beginning to open just as the rebels destroy it, as if the stormtroopers were trying to exit the vehicle.