I feel the exact same way, man. Unfortunately, I think the Internet has ruined the fun that comic book movies used to be. Even in the 90s, when CBMs tended to be lower-quality and even less faithful to the source material, I think the general response to them was more positive overall because fans didn't have an outlet to reduce everything until it barely even exists.
I guess I could understand some of the criticisms of GL if I thought fans and critics held ALL comic book movies to the same standards. Bad dialogue? Excuse me, but that line at the end of TDK where Batman says something like "this city showed you that it's filled with people who believe in good" is one of the worst lines in any movie I've ever heard. Mary Jane's confession that she loves Peter in Spider-Man is so out-of-the-blue that it left me thinking, "Huh? Did I miss something?" Bad dialogue exists in every single comic book movie somewhere. But for the life of me, I can't remember one line in GL that made me cringe, other than maybe Hector screaming like a girl.
But so what? They're just movies, and movies aren't perfect, like you said. CBMs have the difficult task of encompassing decades of stories into 2 hours of so. I've been really pleased with all of our movie superheroes this summer, and it's a shame that people aren't digging Green Lantern. I really do think that the bad reviews made some people walk into this movie determined to hate it. Maybe not, but it's certainly a possibility.