While Fun, It Could Have Easily Been an Expansion
tl;dr: RCT2 has a fair amount of new content; most notably is stack-able scenery. But it wasn't really enough to warrant a full-on Sequel. It could have just as easily been another expansion for the original.
Full Review: RollerCoaster Tycoon 2 is a pretty nice game. It plays pretty much exactly like it's predecessor. It has the same graphics, the same general controls, the same silly peep pathfinding, the same level of Sprite-Detail, etc.
The sounds quality seems marginally better, but only includes a couple new songs that were not in the original. It has several of the same scenery themings from the prior game, but adds a couple new theme-sets. There are also several new coasters, and other rides.
Basically, the new game has most of the content from the previous game, but only adds some new things. The amount of new things added could have easily been an expansion pack.
However, some new mechanics were added that made it way more fun than the previous one. The biggest additions were animated scenery items, stackable scenery, and the ability to build things at different heights than the terrain.
There are some new style of Scenarios this time. For example, one challenge is to try and get your food sales to a certain level by a certain time; another is to try and get your ride sales to be a certain amount for three months in a row.
One of the nicest parts of RCT2 is that it does, in fact, include a sandbox mode. It also has a coaster creator mode designed for just building coasters; which you can save out, and use in your scenarios.
There's even a mode for just designing scenery. With the new stacking abilities, you can build entire skyscrapers, and populate them with food stands, and flat rides. I've even see a couple places in the maps where There's a roller coaster that zips right through the upper layers of a sky scraper. The possibilities have multiplied exponentially with this Sequel!
There's another fun feature too. RollerCoaster Tycoon 2 was licensed by Six Flags. This licensing includes several 'Real' Six Flags theme parks you can play, in-game. There are also a couple Six Flags scenery items, but they are 'meh' at best. But that doesn't mean they're pointless.
All in all, a pretty nice addition to the RCT Franchise.
