Walt is walking nostalgically through his precious drug factory. We see police cars approaching in the background. Badfinger's "Baby Blue" plays. When the policepeople reach Walt, he is sprawled like a starfish martyr, supine on the concrete floor.
A little too picturesque, don't you think?
Walt was shot in the abdomen. I will believe that he is dead when I see a flat line on his ECG and a close-up of his flaccid jugular vein. He did not go from walking around to bleeding-out in a matter of minutes. Nor is there enough blood to suggest it. Walt was lying face down on top of Jesse when the bullet entered him from his right. If the bullet perforated his bowel and he became septic, emergency surgery could still save him. If it seriously damaged his aorta, he would've either died more quickly or still been amenable to resuscitation.
Granted, in an interview immediately following the show, creator Vince Gilligan answered questions that conceded the premise that Walt was "dead." Don't forget, though, that Walter White is one of the greatest criminal minds of our time; a master of deception. Is Gilligan immune? No no; the police scoured the lab for imminent threats, then returned to perform CPR on the still-warm victim.