Playing along with the game, if you're an American there's a mix if you want to do the quality that Europe has to offer, the uniqueness of some attractions and then some weird European things. I'll try and avoid most hypers given to an American, they'll probably just be seen as 'smaller than our stuff'..
Quality Attractions
Taron, Phantasialand
Taiga, Linnanmaki
Untamed, Walibi Holland
Helix, Liseberg
Nemesis, Alton Towers
Lech Coaster, Legendia
Black Mamba, Phantasialand
Balder, Liseberg
Fluch von Novogrod, Hansa Park
Troy, Toverland
Don't think any of these need any explanation.
More Unique Attractions
Pulsar, Walibi Belgium. One opening in America this year (Covid-pending), but the original and damn good.
Lost Gravity, Walibi Holland. There's another one in Germany, but again, the original and damn good.
Vliegende Hollander (aka Flying Dutchman), Efteling. The perfect coaster to capture Efteling's charm, and everyone needs to experience Efteling's charm.
Van Helsing's Factory, Movie Park Germany. Not the best, but really damn good fun and - for an American - shows that size doesn't matter.
Karnan, Hansa Park. If you know, you know. If you don't, don't look into it.
Arthur, Europa Park. Not totally unique, but not in America, and like with Dutchman at Efteling, it captures Europa Park's charm, which should be experienced.
Juvelen, Djurs Sommerland. Again, not unique, but from what I hear, damn good fun and something different.
Weird European Attractions
K2, Karls-Erlebnis Dorf Elstal. This is just a really fun ride with a weird and wacky dark ride section which shows some of the weird surprises European parks can throw up.
Tranan, Skara Sommarland. World's only S&S Free Fly. Haven't done it, heard it's a bit naff, but looks quirky, and one to add to the list.
Rodelbaan, De Waarbeek. World's oldest steel coaster. If you're an American roller coaster person doing a trip with no limitations, you should chuck it in for the bragging rights if nothing else.