As KappaNeko already said below, Gus death was very poorly written. His bodyguard should have noticed the bomb.
Another aspect that I didn't like about this show is I started to like Fring more than Walt. I so wanted Walt to die because his character has turned into this vicious guy losing all sense of humanity and can do anything to save his family. It doesn't matter to him if has to kill a child or a neighbor (checking on his house), or anyone else for that matter. I don't know if that was the intention of the writers, but the villain here seems to be Walt and not the drug dealers.