I think a lot of the teriyaki places (with or w/o burgers) around Seattle are familiy operations and are seldom reviewed. They often include stir-fry dishes and egg rolls and gyoza and the like on their menus. In my experience they make a decent burger but not worth driving out of your way for. I go to one on Greenwood Ave N. & 82nd once and awhile for a cheeseburger combo but while not bad it's not as good as Red Mill or Scooter's in Ballard.
That said I like to patronize these places because I'd hate to have my only option for fast food be a chain restaurant. Nothing against chains but we'd be poorer without family run places.
I agree about the overly sweet teriyaki sauce at most of the places. The original Toshi's on lower Queen Anne, long since gone, had a great sauce. What Toshi does now is start a new teriyaki place and then sell it. When he's still involved it's pretty good but after he leaves the new owners almost always add lots of other choices to his simple menu of only beef or chicken skewers and change his sauce to something they like which seems to be overly sweet.
Seattle Weekly wrote about the history of teriyaki in Seattle in 2007: http://www.seattleweekly.com/2007-08-15/food/how-teriyaki-became-seattle-s-own-fast-food-phenomenon/