The first teaser let some of cats out of the bag: “Arwen is dying”, “Elves at Helm’s Deep”. But it all flashed by so quick the realization was only in retrospect after watching TTT and ROTK. One did gather that the cgi (at least for the trailer) was pretty good. There was debate over whether Blanchett’s Galadriel was beautiful enough (or even beautiful, period.). There was that closeup of Wood as a young pretty boy Frodo which reassured some and outraged others (such as myself.). But the two main things were The Money Shot of the Fellowship, and the confirmation that, yes, there would be three movies. Oddly enough, the inclusion, and thus rabid repeated watchings by fandom, of The Money Shot caused the scene to become ridiculed when it was seen in the actual movie.
The second teaser (actually the first for FOTR), set up the dark tone of Jackson’s LOTR. Also one could see Aragorn the Grunge, and XenArwen.
The last FOTR trailer was probably the best. It had wonderful pacing, like a little movie, starting out light, then dark, then suspenseful, then finishing with a flurry of images, including a very quick glimpse of the Balrog’s foot. (A nice in-joke. An assurance from PJ himself that his version won’t be wearing fluffy bedroom slippers!) I was awed by the Doors of Moria and the Argonath, but the purist in me was slightly disappointed that their appearance was given away. Finally, it’s interesting that McKellen’s reading of the line “They are coming” caused a lot of hysteria on the board as many asserted that it showed that McKellen was a terrible actor, that his Gandalf would be an utter disaster, and that Jackson was a total idiot for not casting Sean Connery.
The first TTT trailer started slowly, ominously, yet quickly swept into the mode of a glorious Hollywood epic. It ended by bringing everything to a stop with Gandalf the White.
The two other TTT trailers seemed pretty indistinguishable to me, but again obviously telegraphed that this was to be a grand crowd-pleasing Hollywood style war movie, with Elves at Helm’s Deep and more Arwen. Any purist going into it had ample warning that they were going to be vastly disappointed.
In all three TTT teasers the reappearance of Gandalf was given away, but really, one wonders if that development would be anywhere near a surprise to even the densest non-reader. Weirdly enough, all the complainers I knew were book firsters who thus aleady knew that Gandalf would return. Bizarre. Also, like with the Balrog in the last FOTR teaser, we were given tantalizing glimpses of two important cgi creatures, Treebeard and Gollum. We only saw the lower part of Treebeard, and never saw the face, and most importantly the eyes, of Gollum. So indeed the trailers teased nicely.
The two trailers of ROTK were pretty indistinguishable. Again, we got the quite correct impression that this was to be a full blown war movie, a massive representation of The War of the Ring. Again, purists should have considered themselves fully warned. And like the FOTR and ROTK trailers, we had a short quiet introduction that swung into full epic mode, ending with Sam’s “Nooooo!” One misrepresentation was Aragorn’s Morannon speech. It was played over the arrival of the Rohirrim at the Pelennor, and I got into a couple of very heated arguments with people who asserted that it was Bernard Hill saying those lines and not Mortensen. There were also some very angry posts on the board since it was apparent that there would be no totally covered helmet for Eowyn, and thus no Dernhelm. Oddly enough, though Dernhelm is my favorite character in the book, I knew how movies worked, and had long took it for granted that disguising Miranda Otto as a man for a good part of the movie just wouldn’t work. (I remember getting into a very hot argument with a couple of purists when I asserted that I, and indeed most viewers, would have been quickly able to identify Ms. Otto by her eyes alone. They hotly asserted that it was absolutely impossible to identify anyone by just the eyes. Purists!!)
All in all, I think the trailers teased just enough. And gave book firsters more than enough warning about certain changes. One does get the impression that the slow start, suspenseful buildup, and furious finish was a deliberate mirror of the films’ structure.
I do note the various scenes in the trailers that didn't appear in the movies, but that's by no means rare. Trailers are usually made before final editing, so a lot of trailers include scenes that ultimately don't make the final cut. It's just what other movies have had their trailers gone over and analysed with a fine tooth comb like Jackson's LOTR?
The last trailer was the Super Trailer, which gives just about everything away. Indeed, it’s almost a Clark Notes of the three films. There are some who say they view the Super Trailer whenever they need a quick LOTR fix. But really, the Super Showings were for the rabid fans anyway.
Good question.