In the intro scene, as Sheppard and McKay are walking down the hall and turn towards the Stargate, they are on the left side. In the next scene with Woolsey, they come from the right.
20:51 mark - after Col. Sheppard and team cease firing, although shotgun shells are strewn about the floor, no one was using a shotgun in the sequence. They are all using automatic weapons. --> Not a goof: One of the SF's (seen at 20:12) is firing a USAS-12, which is an automatic shotgun. It therefore makes sense that there are shotgun shells strewn about.
At 38:53, as the security doors close on Dr. Keller, a couple of film crew members can be seen in a reflection down the corridor.