I'm surprised there are this many die hard Fantastic fans out there. Where were all of you when the comic books got cancelled and the series as a whole was withering away in irrelevancy?
You want your classic Fantastic 4 movie based off the 60's comic? Watch the story films. This movie was clearly trying to reinvigorate a property that desperately needed it. Enough said, they didn't move away from the entire source material they just moved away from a dated series from the 60's and went with the Ultimate series. Reed, Grimm, and Johnny's characterization were pulled straight from that.
The biggest let down, outside of last 30 minutes of the movie, was definitely Dr. Doom. But yet again, if we are looking at the Ultimate series as the source material it's also a drastic change to what you guys are used to. In the Ultimate series Doom's body has been consumed by metal and has hooves.. yes hooves.
I would have loved to see the sorcerer aspect of the character, but we have yet to see that in any major comic book property from Marvel or DC. That is until Doctor Strange comes along in the near future. The lack of Latveria also bugged me but again it's nothing major here. And could have been touched upon in a sequel. Again Dr. Doom himself has gone through changes in the comics.
So to say they strayed so far off the comics is misleading, and just ignorant. They took bits and pieces from the Ultimates, heck even their space suits were inspired by the Future Foundation suits. You guys seem to prefer the classic comic books, which is fine and all. And you have the Story films for that. But they clearly went another way with this particular movie.