The "Tesseract" problem is that it wasn't meant to be a tesseract, but (in Marvel Universe canon) the "Cosmic Cube" which isn't a tesseract at all but [handwaves improbable and contradictory backstories] and thus appears as a glowing ... cube. One lusted after by the dude in the mid-credits interlude. I suppose someone decided that "Tesseract" sounded more cool / less dorky than "Cosmic Cube," but, yes, if they were going to call it that, they should have made it more ... 4-dimensional, I guess. Full agreement on all the positives, and agreement as well on the "stupid gaping bystander" behavior in #6.