I don't understand the "you can't form an opinion of a trailer because you haven't seen the whole movie" mentality here...
It's just another example of defensive fan logic.
You never hear them saying that to like-minded folks, even though what's good for the goose
should be good for the gander. i.e. if someone can't say that the CG or the acting looks sub-par because it's unfinished, then the opposite shouldn't be said either, since what they're so pumped for could be removed or changed completely (once again, I'm looking at you, TASM 2).
The cycle seems to go thusly:
Fan #1: Trailer was awesome dude!
Fan #2: Hell yeah it was; can't wait to see it!
Fan #3: I know guys, the A, B, and C looked soooooooo amazing!
Fan #4: Ehh...that looks like crap.
Fan #5: I agree; I'll probably pass.
Fan #6: Yeah, the X, Y, and Z didn't look too interesting.
Fans 1, 2, and 3: WHAT! You trolls can't say that! You haven't seen the movie yet! That stuff you talked about isn't even finished! They've got about a billion days to fix everything up; it'll look perfect come release day, just you wait and see! Get outta here if you're not content to bow down and worship this magnificent work of art with the rest of us!
Repeat ad nauseum. An exaggeration to be sure, but what's interesting is that the first group is usually trying to propose that the second group is making presumptions, all while making a hell of a lot more themselves (A isn't finished, B will look better, etc.).
People need to realize that everyone understands that the movie isn't in theaters yet. Thanks for pointing out the obvious, but we get it. Everyone is simply giving their impressions on what we have in front of us
here and now. Seems like fans are always content to twist that into a straw-man when they're told something that they don't want to hear.
Jurassic Park is my favorite movie, and I can't believe I'm the one taking up for folks who are apprehensive about the trailer.