If you would like some tips for keeping your park rating up, read on!
I've experimented with the guests' initial happiness level, which can be set in the scenario designer. I've found that the initial setting correlates to the park rating that you initially see once you are playing the scenario. My conclusion is that park rating is based on the happiness of the guests. If you make most of the guests grin, you will get the coveted "999" rating. I've never seen a "1000" rating in RCT2, but did (very briefly) get this in RCT1 - just once!
While peeps are flooding into the park and the number of guests in the park is small, the park rating will tend to get pushed towards the initial happiness level rating that was set in the scenario designer.
Once the number of guests entering the park is small compared to the number of guests in the park, the park rating will then be primarily based on the guests' experience in your park. If your park makes most of them grin, you're in good shape.
The peeps' window can help you evaluate and prioritize your needs. The "group thoughts" view (sound rather Orwellian!) is the most useful. You can see the happiness level of all the guests very quickly by examining their faces.
Sick ones probably aren't too happy about it. First aid stations at the exits of your most intense rides may help a bit.
To get a clear view of the paths, press keys "3" "4" "5" and "6" - in succession, one key at a time. Pause the game and look around. These keys are toggles. Check for vomit and vandalism (the two go hand-in-hand). Make certain you have handyman coverage for all the trouble spots. Dirty paths are one of the most common causes of low park ratings.
If you have guests that want to leave, but can't find the exit, your ratings will take a big hit. This is probably the second most common trouble area. In the peeps' window, choose group thoughts, and see how many want to leave. Click on that row of the list to bring up these individual peeps. Click on a few of them, and see where they are. If a bunch are stuck in the same place, you have a path problem - they will need a more direct route to the park exit
If the guests are complaining about crowding, build more paths and spread out the park with some additional rides in remote places. These paths can be "dead ends", as long as they don't trap the guests. An easy rule to follow to avoid trapping guests on "dead end" paths is to start the new path at your main path and build it away from the park exit. Never make any turns in the direction of the park exit.
You only need one ride on each dead-end path. Add a shop or two and some benches to each path and you will spread out the crowd.
Your guests also complain about crowding if they can't find a place to sit. Make sure you have *lots* of benches, especially around shops that sell food.
Another crowd-fighting idea: If you have rides that always have full queue lines, consider making the queue longer, and add TV's to these longer queue lines. They don't feel crowded while waiting in a queue. They will, however, get tired of waiting. If you see this complaint, and TV's don't solve it, you'll need to shorten the queue.
The guests' attitude will take a turn for the worse if they have multiple problems - hunger, thirst, and bathroom need. They can live with one problem, but several, especially if they also encounter dirty paths, vandalism, or unsatisfactory rides, will cause their attitude to suffer.
The great upward attitude adjuster is, of course, great rides. Match the intensity preferences of your guests, and before you know it, they will be smiling. For most parks this means building a mix of gentle and more intense rides, and distributing them more-or-less evenly in your park. Add some music, scenery and entertainers to keep the guests happy and you are well on your way to the 999 rating!