I'm going to do four, sue me.
1: The Layout
Thorpe Park is an incredibly compact and easy to navigate park, by far the most easy out of the 4 merlin parks. This is great as you don't have to walk too far to get from point A to point B like you do at Alton for example.
2: Flat Ride Collection
Thorpe have the strongest flat ride collection in the UK imo. Detonator is my favourite drop tower of all time, and then rides like Samurai, Vortex, Rush, Quantum, Zodiac, and the bumper cars is a pretty good lineup. Samurai and Detonator being both pretty great rides that are always worth a ride.
3. Nemesis Inferno
Sometimes the smaller inverts are better than the bigger ones. Years ago I would of said it is naff, but I have came to respect it for that great ride that it is.
Smooth, forceful, reliable. Best coaster by far in the park in my opinion.
4. Fright Nights
Fright Nights alongside Tulleys really drove the scare attraction industry in those early years. Fright Nights was the pioneer for a lot of those years. Other events today would not be the same if Fright Nights did not exist, very few scare events came before Fright Nights. And it was the biggest of its kind when it debuted.
I have a love/hate relationship with it nowadays, but it can be a good time, even now.