Well, I tend to like to keep an open mind. But yeah, if you’ve seen trailers for a film and it doesn’t look good, and if you know the previous work of the filmmakers isn’t good, and if critics or people you trust say it’s not good, then yeah it’s probably not good. Even then, you never know, I’ve seen movies that have surprised me. But still it’s usually probably better not to waste your time if the chances are high that it’s bad.
For the prequels, it really depends. There are a lot of people out there who love them (and critics didn’t universally hate them). So yeah it depends. You may hate them, you may not.