Have you seen the original trilogy? how effective were stormtroopers in general? the one time they are super effective is when Vader is behind them at the start. Or sheer numbers when they assault Hoth. They are recruited and indoctinated to be loyal not effective. I think it captures that pulpy adventure feeling very well.
Why they miss:
http://imgur.com/gallery/w5MHii8
Guy has a good point.
In a matter of less than a minute they take a heavily guarded corridor in the Tantive with minimal casualties. They attack a defended position on Hoth without any element of surprise and overwhelm the Rebel defenders in shorts order. Sure they had the numbers edge and weaponry, but defending is always easier than attacking.
Edited by Jo Jo