Disappointing
You have a choice of building from 4 theme park themes: Halloween, Lost Kingdom, and a couple of others. All the rides you can choose from are based on whichever theme you select. Pick Halloween, and your park is dark, much like a Haunted House. Pick "Lost Kingdom", and your park has a dinosaur/Aztec/Mayan jungle theme. You then decide what you want to build in your park: rides, sideshows, shops, and where. You decide who to hire, and then research some new rides.
The UI is one of the most disappointing factors in the game. It's extremely hard to tell if people like your ride or not, and if you're in an information screen, and you select a specific ride to get information on it, it's hard to get back to the main info screen.
Building roller coasters is a whole different story. Whereas in Roller Coaster Tycoon you can either select an already built coaster, or design your own, Sim Theme Park makes you design your own which is an extremely kludgy and complicated process. And if you run out of room while building your coaster, and decide to just pick up the whole structure and move it, forget it. You have to start over.
Researching new rides takes an extremely long time, even with a maxed-out amount of researchers.
You must assign janitors, mechanics, and guards specific routes to cover, so a janitor just won't head over to a mess unless someone specific has been assigned a route there. And if you have 2 overlapping routes, it's extremely hard to tell which staff member covers which route.
For those looking for a good roller coaster sim, skip this one, and grab Roller Coaster Tycoon instead. This falls short of expectations.