I definately put "Good Service" at the top. I don't care if the park is immaculate (well, actually I do) but if every employee/cast member makes me feel like I'm unwelcome, then I most definately won't be back. Cleanliness is a very, very close second. If the park is filthy, then not only is it not asthetically pleasing, it would suggest safety hazards. Also, cleanliness would generally follow from good service. Last, but nowhere near least, is ride quality. The rides have to be good quality, not puke-your-brains-out while going 100 miles per hour in a completely unthemed steel cage. It's just not appealing to me. However, each of these three elements need to be present in a successful park. One thing that stuck with me when I went to Universal was that the employees weren't nearly as friendly as they were at Disney. I did go on some very good rides that day, and the park was very clean, but what I remember most is the disposition of the employees.
And yes, I do hold every park to the same standards.