Pleasant:
The Comet (HersheyPark) - Very nice rollercoaster for being an "old" coaster, tons of fun and still my favorite woodie in the park.
The Big Bad Wolf (R.I.P. - BGW) - Although I only rode it once, was very sad to see it go. This was the only suspended coaster I'd been on and it was really a cool experience. The other coasters of today just don't have the same feeling.
Kumba (BGT) - Still one of my favorite all time steel coasters, the place of the inversions and pacing of it is very nice, love the tunnel at the end.
Un-Pleasant:
The Wildcat (Hersheypark) - I've rode this coaster twice....about 6 years apart, and both times felt like I had just been in a fight....way too rough, even toward the front.
Reese's Challenge (Hersheypark) - I heard bad reviews about this shooting dark ride, but OMG, it was worse than I ever imagined, just completely dull and almost no sense that you're hitting anything or things are happening.
Dinosaur (WDW- AK) - I do love Jurassic Park at IOA, but this ride is too loud and dark to impress me...its just more annoying than anything, plus the fact that WDW should have gotten its own Indiana Jones ride.
Mission:Space (EPCOT) - First, the final product is a severe disappointment compared to what was planned originally. Second, the entire idea of the attraction is motion sickness just waiting to happen. While astronauts do experience centrifuges and simulators, I really don't think they experience both at the same time and they're highly athletic. Average WDW guest isn't and we see the results.
But THE most unpleasant has to be:
High Roller (Stratosphere Tower- Las Vegas)
I rode it at night and it was probably the only rollercoaster that scared me, as it was sooo rough and felt like it was falling apart....vowed never again to ride it and now I don't have to.