well these are the Theme parks that i have visited in Europe
1) Thorpe park ( near London )
this is a very gud park, has a few rides, but all of them are good, and it also has Europe's highest water slide ( in which u sit on a boat )
2) Chessington ( near London)
has plenty of scary roller coasters, did not like the park very much though, still not a bad experience, if you are looking for some roller coaster rides at a cheap rate.
3) LEGO LAND ( Düsseldorf, GERMANY )
this is a unique park , it has whole miniature cities made with lego, and has really fun rides, and this park is for the faint hearted, it does not have scary rollercoasters and stuff
4) DISNEY LAND PARIS
this is a daddy of all parks, has a lot of roller coasters, and thrill rides. no need to visit other parks if you go in this one, will take 2 days to sit on most of the rides.
and the places i would rank them in the following order
1) Munich
2) London
3) Rome
4) Paris
5) Brussels
and please avoid Amsterdam ( for reasons that cant be disclosed over here on pakwheels )