The times in which they were released is the only real difference between em, they are all basically just newly engineered molds of classics characters. edit: wiki will tell it better http://en.wikipedia.org/wiki/Transformers_Classics
Classics and Generations are far more driven by new molds (who yes do get reworked of course) Universe has a far higher percentage of old figures just repainted into new ones (usually) not of the same line following those trends, Classics/Generations usually have far.. newer engineering than Universe as well. none of the above is absolute, just the general trends.
See above. The first Universe line was virtually all repaints of previously existing US Transformers like Armada and Beast Wars (with a previously Japanese-only mold or two seeing it's first US release, like the Nemesis Prime repaint of Takara's Big Convoy). Later came Universe Classics, which kicked off the line of updated versions of "classic" characters. That morphed into the return of the Universe line (Universe 2.0 or Universe Classics, the terms are used interchangeably) keeping the trend going with new molds (and repaints of those new molds) of those classic characters. Generations and Reveal the Shield have continued that trend, while bringing in some more obscure characters (comic book creations like Drift and Straxus/Darkmount that had no toys previously, or Skullgrin and Thunderwing, who've been virtually ignored in the toy department since their G1 releases until now) and the War for Cybertron toys as well (since the video game didn't spawn a line of its own, the four molds that were created were released via Generations). Takara grouped the Universe Classics and Universe 2.0 into the Henkei Classics line (with a few exclusives, some of which haven't seen a US release and probably never will), and their upcoming United line is basically Henkei 2.0, with the Takara versions of the Generations and Reveal the Shield toys. There has been no Takara counterpart of the original repaint-only Universe line, however. But yeah, Wollstone covered it much more succinctly than I just did.
Generations, deluxe figures 'only'(?). Classics, mostly deluxes but voyagers as well. Universe, all size classes. I'm not 100% this is correct, but to my knowledge, that's a difference between these lines.
Classics was a filler line that found itself to be insanely popular, created in the delay of the first live-action movie. After the Movie-1 line died down, Hasbro rebooted the Universe line to also include new molds based on theme set by the Classics line. Then the line was called finished for the RotF push. Generations is part of the revival of the theme, but the line is set at the Deluxe scale/price point. Some of the theme is also hitting shelves in the "Yellow Box" line, in the Reveal the Shield promo.
Just the names to infuse new marketing life into the toys. They're all the same in so far as bringing back random toys from other lines and redesigning the vintage stuff to update it and keep the nostalgia/adults appeased. No need to over complicate it.
In all fairness universe 2.0 voyagers were mostly redecos. They had plenty of new deluxe and ultra molds!
Classics, 2006, included Legends, Deluxes, Mini-Cons and Voyagers. Mostly new molds, but Legends and Mini-cons were sometimes repaints. Henkei! Henkei!, 2006-2008 (Japanese line). Includes repaints of Classics and Universe original molds. Universe, 2008, included Legends, Deluxes, Voyagers, and Ultras. Mostly repaints of Classics and Cybertron toys with a few new molds. Generations, 2010, Deluxes only. Almost entirely new molds but some repaints of Classics molds. United, 2010 (Japanese line). Includes practically all Generations toys along with some Reveal the Shield characters. Reveal the Shield, 2010-2011. Legends, Scouts, Deluxes, Voyagers (first to include movie and G1 characters.) Quite a few new molds but some ROTF, NEST and Generations repaints.
Generations includes legend class as well (if I'm thinking the megs, laser prime, trailcutter are generations) and minicons. I think body on robot modes are remolds of seeker classics too. Also I think the seacon reissue falls under generations. I could be wrong, but I think I just saw that on the database here.
...only the voyagers from Universe 2.0 were repaints (+new mold Inferno), the Ultras and Deluxes were all completely new molds IIRC
They're all lines dedicated to homaging the past. And they've given rise to a moronic acronym used only by the most feckless collectors.
Pretty much this. There are details like what size classes and prices points were available as well as the eras they encompassed but Wheeljack Prime pretty much nailed the most basic difference of the three lines.