I sort of see his point though. Spider Man 3 was so bad that it retroactively made Spider Man 1 and 2 bad for me. Now I can't unsee the ridiculous amount of cheese in the Raimi movies. I also liked the first few Donner Superman movies but after watching Superman Returns I couldn't stand the Donner universe either (I can't wait for the Superman reboot by the way).Actually I'm really not sure I agree with the premise that a disappointing sequel can negate the quality of what came before. Even with the most egregious example of a drop in quality, Star Wars, I don't find myself enjoying the first films any less. It seems a really odd thing to argue.
A lot of people feel this way about the Mass Effect trilogy.