I haven't found a game that has captured the same feel as the original Rollercoaster Tycoon. It's probably just notalgia, but I don't think I will ever enjoy a game like that to that extent ever again.
The man keeps us down because he likes to see us frown
I find it really weird that it's so hard to find a game of the same genre and quality of Roller Coaster Tycoon. I'm with capgamer in a sense-- RCT is not my favorite series, but I've definitely never played anything in that genre that I feel comes close to it.
I don't get the dislike for RCT3 though. I think that game is easily on par with the rest of the series.