Because it changes with who I am going. I believe your best customers will be the ones that come every year. I never repeat a house, or at least I haven't so far. For me, the bedrooms are key. Having enough baths and bedrooms, and at least one bedroom off by itself with a bath (for the grandparent's quiet factor.) Then I look at location. I won't drive further then 12 minutes. Weird time, but that is my cut off.
Then I look at extras. I love a computer with internet. A TV in every room is nice. A few toys so I don't have to bring any in a range of kid's ages. Board games & a playstation with a few games.
A coffeemaker in the kitchen with the filters that match (SO irritating to have to buy these every vacation, use 7 and leave the pack, plus the first day you always have to use a paper towel!) Also a vacuum sweeper for the house (not locked up.) Then, I must admit, I like a well stocked kitchen, utensil wise. We actually do cook on vacation and I enjoy a non stick pan or two, at least 2 cookie sheets, one 13x9 inch pan (for boxed brownies

) and lots of bowls for storing leftovers and fruit in the fridge. And a few basic spices is nice, but perhaps people don't do that because they get used up and must be re-bought. I've been a few places that have salt/pepper/cinnamon/garlic powder/sugar in big containers. It's just a nice touch that couldn't cost that much money.
And the washer and dryer must work. I've been to two houses where one was broken. Totally unacceptable. We made such a fuss, the poor housekeeper came and did the laundry at her house (she was going to do it for free but we all felt horrid so tipped her WELL, but there was no way I was spending a minute of my vacation at a laundrimat!) I stay off site so I have a house and basically just want house things.
Older kids do enjoy a game room with pool table/foos table/ or ping pong. And the men enjoy it too to escape and drink their beer. Having little kids, I never use them but someday I'm sure I will.
A Disney themed room is never a bad thing. Especially a girl on and a boy one. Or a Nick room would be good too. One Nick room and one Disney would be perfect for our family.