A random assortment of stuff:
1) The placements of your lights should be important. Guests should complain about it being too dark at night in inadequately lit sections.
2) Also, it'd be neat to see evening views of the park (ride lights, shop lights, path lights, etc...)
3) The ability to set park hours & operating schedule.
4) Time flys by too fast in the game! (And when you're playing the game...)
5) It'd be neat to go year-by-year. At the end of the operation cycle the park empties, and you have the winter months to build new attractions, or make changes to the park. (You could even advertise opening dates for the ride, then keep it closed to smooth out the track, thus annoying your guests... ;) If you didn't want to make any additions, or were done making additions, you could possibly skip time ahead to the opening of the park.
6) Most of the other things that have been stated here.