I've never played the Roller Coaster Tycoon games although I have seen a few cool YouTube videos of rollercoasters made in it. I'm impressed that the original game was mostly written in assembly to get maximum performance.
First 2 games were really groundbreaking at the time. 3rd game was great foray into 3D. Thrillville is the 4th Roller Coaster game by Frontier, and it was a bit different since you couldn't fully customize the park layouts, but I believe the sequel/expansion let you do so. And it had a fun and unique system where you could converse with park guests. And now we have Planet Coaster and Planet Zoo by Frontier which are amazing. I also love the Theme Park series by Bullfrog if you haven't tried those. Very dated, but I felt the business management aspect was always better than the RCT games.