Mars was one of the first places I tried as soon as I moved into the neighbourhood, and I haven't stopped going back. Of course, you can't eat at Mars regularly unless you enjoy the consequences of a poor diet, so when I say I keep going back, I mean it's the first option after a night of drinking and general merriment.
The menu is pretty extensive. Most of it is good, greasy diner food that we all know and love. I tried being adventurous once and ordered a hamburger sandwich and didn't like it too much. I also tried their steak and eggs and it was just okay. I stick to the corned beef hash, cheeseburger or eggs benedict (they have really good hollandaise sauce) and they have never failed to satisfy.
It gets busy during weekend mornings, but I've never had trouble scoring a booth in the late hours of a Saturday night. The waitresses are very friendly and the service is quick. You can also order takeout if you prefer to pass out at home immediately after eating.
I try not to go to Mars during the day in the summer though. It can get pretty hot inside the restaurant.