Disclaimer: Me and Denny's go back a long way. Decades, in fact. So this review is totally biased by emotion.
Denny's is my gold standard for all day breakfast. It never fails in quantity, freshness, perfect easy over eggs, and OMG the pancakes. And bottomless coffee that actually wakes me up. And colourful menus. And low prices. The dining room has always been clean at all the locations I have ever visited across North American over the years. Denny's formula, as stated above, is consistent yet the menu has evolved to include healthy options, such as grit and oatmeal. The dinner menu has a wider offerings as well, though I confess that I also order breakfast when I patronize for dinner.
I don't even know if I can wholeheartedly call it a greasy spoon, cause there are so many items that don't fit that name. Still, Denny's is the all-day-breakfast love of my life.