Kings Dominion isn't usually like that at all. I agree with Phil, it's not the best park in the world - far from it, but it's still good. There's a few great rides and a mixture of meh-poor ones. Like Phil says, that's still better than most UK parks.
In fact, I can't recall any major issues or complaints to be made about Kings Dominion and I went like 5 times last summer. The only real trouble with it is the lack of shade, the trouble they were having with Intimidator and Volcano's death-queue. Oh, and Dominator's lack of zero-g is worth booing too.
I think I only spent a couple of full days there, but I actually really like Kings Dominion of an evening. Turning up at 7 pm on a summer evening when the park is dead, cool and twilight sets in at about 8-9.
I think it goes to show how one bad visit with a large group of enthusiasts can effect a park's rating. I don't doubt that on the day TPR last went was probably dire, but it's such a shame I've heard nothing good about KD ever since.
As for my own worst experiences, I don't know... but my trip to Kennywood and Europa left me thinking both were no where near as good as you hear about, yet there was nothing to complain about outright with either. They both just felt a bit ****. Kennywood felt a lot like Blackpool, only absolutely ****. Their woodies are all exceptionally poor and the locals... :| God, I just.. where do I start? I felt uncomfortable at Kennywood. I don't know if it wasn't for my first experiences of Blackpool being so magical I'd think the same of there? Quite possibly and it again shows what importance a first impression has. With Europa... it's a pretty park filled with exceptionally poor rides and everything about it was meh, just not a reflection of the hype at all. But again, possibly just a bad visit. It will be interesting to see what I think when I return to these parks.