Interesting to see such a list for once, though it centers purely on fairly recent Hollywood stuff. I also don't like RottenTomatos very much, but I visit their page from time to time to read something by a few american critics.
It's interesting to see so many films assembled I am sooo not interested in. And I guess I'm not alone with my opinion. 

I have actually seen no. 65 Boat Trip with Oscar winner Cuba Gooding Jr. It was a private screening with a couple of friends and we had already been prepared for the worst by a friend who said that the film was so hilariously bad we just had to see it. Well, it was even worse - but enjoyable. A typical case of a film that's so bad you simply can't belive your eyes.  Definitely qualifies for my personal worst films ever list.

I have Gods and Generals on DVD at home and plan on seeing it despite the negative press. 

Don't know what's so bad about no. 30 Darkness by jaume Balaguero. In Germany the film got very positive critical responses, and though i wasn't impressed I found it to be a good film. A friend of mine even considers it one of his favorites.

Rollerball by the usually great John McTiernan which is no. 20 also isn't that bad. It's just one of those films that don't make any sense at all and you wonder why they have been made. I only borrowed it from my local videostore somewhere in 2003 I believe, because a good German critic praised it because of its innovative editing. I must agree that the editing alone is worth the watch, though contrary to him I found it completely confusing and incoherent. I am still sure the film as it was released was a rough cut and Tiernan wasn't allowed to complete it. But maybe I should watch it again. The editing is definitely a curiosity as I haven't seen anything like it ever since. But I guess everybody ought to decide for themselves. But the editor of Rottentomatos isn't far off when he says that the script was possibly written by monkeys. 

I must say I've definitely never seen less films from a top list than from this one. Probably also the first time that's a good thing.