Living in Northern NJ and being able to go to both Dorney Park and Six Flags Great Adventure, I would like to comment on both.
Dorney Park:
I wen there last year for like the 10th time on my Senior Class Trip. Let me just second what MBurk said, they have greatly improved their rides. They have two brand new, high quality coasters, Steel Force and Talon, both awesome, and they have cleaned up the park nicely as well. I personally don't see them trying to even compete with WDW because they are a seasonal park and a VERY local one at that. The water park is great also.
Six Flags:
Last time I went was 2 years ago. I personally don't like the park that much for two reasons: Pricing and Crowds. I went for Physics Day back in Junior year, and it wasn't that crowded which allowed me to actually enjoy the park and look at the surroundings without going bizerk trying to run to all the good rides. What they do have is really awesome coasters. Granted they spend about zero time with theming, they make some mean rides. As for them competing with Disney, they do try to, but will never get therel; they have a frontier themed area that just pales in comparison to Frontierland, it's just plain sad. The park usually looks pretty sad and could use a fresh coat of paint. I haven't been able to try their version of fast pass but my friend used it last year and said u need to wait in line when u get to the park and pick which rides you want it for and pay for it. I don't really know though. One last comment and then I'll stop rambling: Remember Six Flags is run by/in conjunction with AOL/Time Warner which is a company in direct competition with Disney at every level so that's why they have so many damn parks and try to outdo Disney. They never will of course.