In terms of rides that are unique to Kennywood:
- Noah's Ark is a must do classic fun house with a very unique rocking boat.
- Old Mill, classic dark boat ride
- Turtle... last of it's kind in the world. Not the most thrilling, but really needs to be experienced at least once... it dates from 1927!
- Kangaroo, another classic ride that dates back to 1962. The original Mega Jump
- Spinvasion, the only Zamperla Gryphon flat ride in the States
- Jack Rabbit, from 1920... that double dip is really something, especially in the back (if I'm not mistaken)
- Phantom's Revenge and Steel Curtain (if it's open, fingers crossed)
- Whip, which are bit more common back East, but pretty rare on the West Coast
- Thunderbolt, classic wooden coaster, and Racer, a rare wooden mobius coaster
In short, they have a lot of rides you really won't find anywhere else. Exterminator is worth a ride as well... although it's a standard Reverchon spinning mouse, but it's placement underground with some effects (and a wild queue!) makes it memorable.
For me, Ghostwood Estate is a pretty standard Sally Dark ride, aside from being located on a second floor... so if you've done them before, I think that's something you could skip.
Last time I was at Kennywood, it was when Steel Curtain opened. Hoping to stop by there again briefly this summer, just in time (hopefully) to catch it open again, haha. And really looking forward to riding Spinvasion