My 2 cents, as a
huge RCT fan (and Transport Tycoon before it
)
The building tools are incredible - absolutely second-to-none, you won't be disappointed in the slightest at what you can build and all the options for designing your rides and park...
BUT it is severely lacking the other part of what I enjoyed about RCT - the management aspects are extremely watered down to the point they are virtually non-existent. Making money is trivial, keeping the park running smoothly is a complete doddle and nothing even remotely challenging ever happens (unless you go out of your way to make tons of bad decisions to create problems)... part of this is due to the fact that the maximum size your park can get to (in terms of number of guests) is not that large (maybe 1,000 people at the very maximum) so the park never feels like a "massive" park to me...
So it depends what you're looking for... as a sandbox builder it's incredible, as a
game though I'm not so convinced (and I think it's because of that I played it a lot when I first got it but quickly dropped it and didn't go back, yet)