> OpenRCT2 requires the original RollerCoaster Tycoon 2 game files
I think a lot of the charm of RCT2 comes from the specific assets in use and the degree of whimsy and joy they contain, more so than TTD's matter-of-fact trains and planes and such.
It's not like these folks are setting out to make a totally free-as-in-beer game that replaces the old one; they just want to be able to fix bugs and add features, and you can't easily do that with the original retail stuff.