Taking them one by one:
-The negative impact of the first movie
Yep... big impact. The first movie wasn't outright horrible, but it was as mediocre a movie as you can get. It had it's good moments, but they were really tough to find in all the bad. The extended edition DVD made it a more cohesive story - but it didn't remove the bad taste I got from the original theatrical release.
Then you take the same actors, writers, director, and producers for the sequel and the recipe for disaster was there. People took what impressions they got from the first one and it crippled the expectations for the sequel. They simply expected more of the same.
Another knock against the movie. While the FF certainly can and should have been able to compete with the current crop of movies - Fox's FF just can't. It's not strong enough a property to be put up against those other movies. The way these movies have hit... you have a 2-week window for success.
FF would have been killed if it opened on the same weekend as Spider-Man, Pirates, Transformers, Harry Potter.
Not 100% sold on this. The action and quiet moments weren't too unbalanced. Then again, the movie's length contributed to that. I'm sure that any cut scenes from the movie would be character development ones and not action sequences.
Biggest problem with the action scenes - nighttime. That whole pursuit of Doom sequence was muted in the darkness. That was the same problem I had with the ending to The Hulk. You need to see the action to appreciate it. The stuff at the wedding was fine, as was the scene in London and the scene in the mountains when they capture the Surfer.
-seeming small in scale compared to the rest of the summers big hitters
Surprisingly true considering they were dealing with the complete destruction of the Earth. The threat of destruction wasn't realized until the last 5 minutes of the movie. At least with a movie like Armageddon, you knew from the very beginning of the movie that Earth was doomed.
-Improved but not enough for people to care after the first
Very true. Again, it was too much a case of "more of the same".
Some other things....
I REALLY wanted a sequence or montage to show just how the FF became the celebrities they're portrayed as in the movie. They show Sue being concerned about raising a normal family in the midst of all the extraordinary circumstances surrounding their lives. Sorry... but I didn't see anything extraodinary about their lives prior to the arrival of the Surfer.
They could have done a cut-scene montage where they showed newspaper clippings, magazines, TV news reports and the images could have come from classic scenes and covers straight off the comics page.
I know I was underwhelmed by the first one. The second fared slightly better in my eyes. In both cases, I feel the creators didn't strive to create the best movie they could.
In the end... I want to see the Fantastic Four, not the Tepid Four.