One of the coolest new things brought to the screen in The Empire Strikes Back were the Imperial Walkers, now known as the AT-ATs (All Terrain Armored Transports). These gigantic walking tanks deployed on Hoth were like lumbering animals. They were also, in retrospect incredibly slow, inefficient, and revealed a serious logistic flaw on screen, but visually, they were amazing. Like the dogfight sequences between the X-Wing Fighters and the TIE Fighters over the Death Star in the original film the ground battle on Hoth in Empire was spectacular.
There was also some controversy regarding the walkers around the time the film came out. It seems the design was based on (some so too much so) a four-legged, gyro balanced walking cargo transport vehicle designed by Syd Mead for U.S. Steel in the 1960s. Mead's Walker was based on elephant anatomy down to foot pads that expanded when pressed down and contracted when raised in order to keep the feet from getting stuck in mud or snow. The feet could also be rotated and locked to form wheels for rolling over smooth terrain. Mead also created a similar vehicle for use on the moon.
I'm not sure how the whole controversy panned out. I do know that AT-AT designer Joe Johnston has acknowledged the Mead painting as what inspired his own design.
There were prior versions of the walker that didn't walk. One was a giant treaded ground tank. Another rolled on sets of huge wheels.
While not used in The Empire Strikes Back, this wheeled version found it's way, intact, into Star Wars: Episode III - Revenge of the Sith as the HAVw (Heavy Assualt Vehicle wheeled) A6 Juggernaut, also known as the Turbo Tank. It can be seen several times during the battles on the Wookiee homeworld, Kashyyyk.
Back to the AT-ATs. Were these vehicles the best design to bring to an ice planet? They move slowly. They're legs are close to the body and don't really splay out much for added stability when needed, and to distribute the vehicles weight over what could be treacherous "ground" beneath them. Any air pockets in the ice they're walking over could land one deep in a crevasse. Again, they are also really slow. Wouldn't a hovering vehicle, similar to a landspeeder, work better?
While the blasters on the snowspeeders weren't strong enough to penetrate the armor of the walkers, would torpedoes have been able to do the trick? Probably. If the Rebels had mounted missile launchers on their snowspeeders, the battle would have been over much faster and the Empire would have lost. Of course, the movie shows that while the armor may be too tough to penetrate while the walkers are walking, knock one down and it takes only a couple of shots with those same blasters to blow one up.
The real answer to the Imperial Walker problem on Hoth came from a cartoon that was published in Starlog magazine shortly after TESB was released. I couldn't locate it in time for this post (it may have accompanied David Gerrold's regular column). In the cartoon, the Millennium Falcon is used to bump the walkers from the side, breaking their knee joints and causing them to tip over sideways. If you had several walkers lined up, you could tip them like dominoes.