HORRIBLE. The worst part is the service. Those waitresses are NASTY. They simply don't care. The prices are creeping up to what other restaurants charge so the savings is Not worth the aggravation. The food is edible--this is the best that I can say about it. I like to support 24/7 restaurants and so I went for a while. I will not be going back. The main thing, though, is the rude service that you are forced to contend with. And there are plenty of servers there so it isn't that they are swamped. For the most part, they like to huddle behind the counter and laugh and giggle while you wait. Try getting a thank you from whoever takes your money at the register--you won't.
I know some have had good experiences here and I would say that I used to about a year ago. But it has changed significantly. Denny's has some good food, reasonable prices, you can use coupons, and get stellar service with a smile.
My recommendation is don't go here. Even if I were to complain to the management--remember--bottom line is They Don't Care!