Charming, responsive, streamlined, and satisfying, with tons of mini-games and compelling missions. In a nutshell: FUN!
The mini games, which really are the soul of the game, are fun. Some are especially snazzy, like the sharp looking circuit boards you train the technicians with. It has a very addicting memorization game where you connect circuits together with pipes. Other mini games are more basic looking, but regardless, they are solid and well implemented. Racing dune buggies, for instance, feels as natural as in a game like Mario Kart, and the side scrolling bike racing game has funky physics and groovy visuals. A real standout is the first person shooter game, which has excellent graphics, with dummies for enemies and a variety of cork guns. It definitely feels like a real shooter and is fun!
Everything is streamlined and the UI is informative. Although loading and saving games is a little slow, and the music in the game is too loud (and strangely the movie cut scene volume is tied to the music volume setting, so turning down the music means you won't hear what the person says during the movies!), everything else is seamless and responsive. Building rollercoasters, adding food stalls, interacting with guests, who are fully voiced BTW, are all extremely well done.
In the end, Thrillville: Off The Rails is just one of those wonderously next gen experiences. It's like someone finally figured out how to make a good tycoon game. Frontier has been doing this for a long time, and it looks like they've really taken the experience they've gained to heart and have used it to fine tune the game play so as to present a charming and interesting game that is strangely compelling.
I played the game on the Xbox 360, so your mileage may vary.