I would love to see a game where you can build your own coasters, or even a game where you can "ride" pre-made coasters. I don't know what roller coaster tycoon is though (I've heard of it but never played it). Is that more like a simulated theme park where you make decisions to make money etc?
Yeah it's more of a decision making game where you do build the theme park but you have to do it in a strategic money making way. There is an open world option though where you can just build a park for fun without objectives. Theme Park World on the Playstation had a feature where you could ride the rollercoasters you built in first person, Tycoon probably has it but can't recall. Rollercoaster tycoon does have enough options to make it pretty much seem that you are building your own rollercoaster, you can place the tracks where you want and set the colour, theme, name, speed, carriage type and size etc etc. Mechanics for riding a 3d coaster is going to be pretty tough in C2 haha, even simulating it in 2D sounds difficult. Also see one of the above posts, the game Planet Coaster on Steam looks like it is doing well and has this kind of thing in full 3D.