Yes, 4 stars for Denny's. Why? Because it's damn good for what it is. Good, quick, cheap food at any time of the day. If you get sick from food poisoning, find a pube in your meal, or your server snorts coke in front of you by rolling up one of your pancakes, then yeah, give it one or two stars. But you walked into Denny's knowing what it was, right?
The staff was friendly and efficient. Almost too efficient - a crowd of people were waiting to be seated as a crowd of people were waiting to pay. The food came out quickly and it was your typical budget diner fare. No surprises here. The prices are among the lowest that you'll find for restaurants on the strip and it'll give you the energy to walk around on a hot day.
Also don't understand some of the reviews where people act like coming here late night / early morning after partying is a bad thing. I think it's a great thing. Denny's is a good way to recharge after a night out. There's no shame in that. Unless you're a girl with four guys, walking around like you're a cowboy. Then there's a little shame in that. But it's Denny's - nobody will judge you.