IMO the Best Diner in Worcester. It's actually been renamed "The Sisters Diner", but the quality remains excellent.
While the quality of the food is excellent it's the variety of the menu that makes this place stand out. There's a wide variety of types of "Eggs Benedict" several creative omelets with fresh ingredients. My favorite by far though is the Cajun Shrimp omelet. It's perfectly spiced with large shrimp, sweet sauteed onions, fresh red peppers, and cheese. They're often trying new specials here, including virgin bloody marys (not a fan myself, but the kitchen is always experimenting and often coming up with surprisingly tasty results).
The reason you probably haven't heard of this place is that the hours are severely limited. I think they close around 1 PM or Noon on the Weekend, still it's worth getting to this tiny out of the way treat.