A lot of places are busy during the summer -tourist- season, but this restaurant is hopping throughout the year because the food is good, the dress is casual (or fancy, if you like for an evening out), the drinks are strong, and the view of the water is terrific.
You might want to try it at lunch time, if you don't like crowds. You can enjoy the wonderful lake vista and eat a hamburger or a steak, or something in between. Not a huge menu, but standard fare options. Note that the menu is the same at lunch or dinner- no cost savings, but not terribly costly anyway.
Stop by Duffy's on your way out of town for a drink. The fellow who suggested that bar was right on the mark, though I CAN NOT speak for the accomodations at either of these places.
Mars Restaurant (and "Resort")
W4098 S Shore Dr,
Lake Geneva, WI 5314