I like that you can do things at your own pace. In fact, if you expand your park to include more species, etc., you increase the difficulty yourself, as well as adding more dangerous dinosaurs.
In other words, it progresses at your own pace. I like the level of detail, the behavior, the customization, the voice acting, the music... it's fantastic. What I don't like is that they include so much DLC. I prefer to buy the full game rather than have paid content patches (which I won't pay for because I don't support this method).