Here's what I want to see:
A old fashioned "classic view" (lo res graphics like RCT2 for older computers) and of course, the 3D view, as a selectable option
Natural disasters. Real parks are attacked constanlly by rain, tornadoes, hurricanes, lightning bolts, etc etc, so why not the game park? You should be able to turn this off and select which disasters you want to happen. Say for example a really bad storm brews overhead, and all of the sudden a bolt of lightning bursts from the sky and strikes a coaster car, causing the electrical system of the coaster to mess up, and kills some people in the car. lol
Classic RCT music like the dodgems beat in a updated style.
A expanded online mode. Create your own "visitor", male female boy or girl, give him/her some money, say, 200 bucks, type in a IP, and visit a park in online mode. Go to the front gate and pay the enterance fee and walk through the park, buying things and riding rides.
Ride restrictions (you must be this tall to ride this ride)
Different enviroments (i personally would love to be able to build a theme park on, say, the low gravity of the moon, or, unrealistically, but still fun, on the sun)
if I think of more I will post.