Parc Astérix, especially if you like rollercoasters. There are fast pass bundle options for a lot of the main rides as well. Halloween is also a great time to go, they have a bunch of great haunted houses and the park is open after hours.
Liseberg is pretty good.
Grönalund in Stockholm is also good.
The two parks have a very different vibe.
Liseberg is a big park with the rides more spaced out while grönalund is a small space with the rides literally overlapping with each other.
You can expect to wait an hour for a coaster on full days... But it helps to go early in the morning. And ride less popular coasters. Also in the evening, I remember riding silver star with 10 minutes queue time.
Is this the park somewhat close to Cologne (Köln)? I ended up there once by accident while backpacking and took basically a random Flixbus. Looked nice indeed!
(I don't recommend taking random Flixbuses for amusement)