Personally, there's a few out there that I think every enthusiast should go to:
1. Cedar Point, America's True Roller Coast: Just in general, this park is a living, breathing, coaster museum with a ton of historic feats and attractions being housed there. Plus, it has some of the best coasters in the nation, you simply can't beat a line up with Steel Vengeance, Millennium Force, and Maverick. Plus, it has arguably one of the best beaches, primarily because of the views of the coasters behind you.
2. Knoebels/Lakemont Park: I'm going to lump both of these parks together due to the proximity and just similar vibes therein. Knoebels has Phoenix and Twister, which honestly speaking, Twister should get a lot more love than what it receives because it is extremely close to Phoenix IMO. Lakemont Park, you have the oldest coaster in the nation, that park is a legacy and should be more frequented because it is a precious landmark that is honestly legendary anymore.
3. Knott's Berry Farms: Alright, I'm going to be real, this was a hard choice between Carowinds, SFFT and Knott's, but Knott's held out. It is honestly the true success story from the west, what was once a farm for boysenberries, became a whole theme park that is honestly the best theme park out there. With spectacular theming, world class attractions, and food that can satisfy even the most critical thoosie, Knott's has a history that it hasn't let go of and chases with every addition they have.
4. Kings Island: Kings Island, while in modern terms is behind alot of parks, for historical reasons still ranks high up there. KI has a legendary, albeit mostly rough, wooden coaster line up that is almost hallowed with the wooden coaster length record. This, coupled with three very popular B&M coasters and a diverse blend of classic Arrow's give the park an edge and definitely gives people an excuse to come up. Oh yeah, and the blue ice cream.