Revision seems the correct description of 3.5. You still had the same classes, you still had basically the same game. Comare that to 2E where they took our whole classes, reorganized the classes and rewrote all the text (taking out significant GM procedures and advice.
It wasn't like 1E to 2E where you switched from attack matrices to THAC0, made NWP a major option the core book, removed classes, made signif cant changes to classes, rewrote pretty much all of the text and took out large chunks of the exploration rules.
Because I wasn't using those GM procedures or following that GM advice, at least since 1986 and the release of Oriental Adventures; and because I was using weapon specialisation from UA and OA and was using non-weapon proficiencies from OA, WSG and DSG, I didn't find the move from AD&D to 2nd ed AD&D to be a big deal at all.
For instance, I was able to play with almost complete rules mastery in 2nd ed AD&D games without ever having read a 2nd ed AD&D rulebook. The only exception to that claim I can think of involved initiative, and that took one go to learn. (The unarmed combat rules were different, too, but they never came up, much as they had rarely come up before.)
Similarly, I was able to GM players who had learned to play from 2nd ed AD&D books, and were using PCs built from those books.
Of course the classes were a bit different in places: more spells for illusionists, different bards etc. But I was already used to different classes from Dragon magazines, including the revised bard that was published somewhere around issue #60. And THACO already existed in the DMG list of monsters (Appendix E, I think it was) so the only difference that made was in relation to the 6 natural 20s, which applied to ACs that rarely came up unless you were GMing the D series, and which in any bit was always an obscure part of the rules, to me at least.
So for me personally the change was no big deal at all.
You *can* sit down to play with three players, who have made characters using 3e, 3.5e, and Pathfinder, and play for quite some time before someone goes, "Wait a minute, what rules did you make that character under?"
There's really nothing that would stop you from bringing a 3.0 character sheet to a 3.5 or even PF session
I think this is equally true for 1st ed and 2nd ed AD&D PCs, as [MENTION=2205]Hobo[/MENTION] has pointed out.
It's also probably pretty true for HARP and Rolemaster PCs, for Runequest, Cthulhu and Stormbringer PCs, and for that matter for Stormbringer and Elric PCs. There are lots of games out there where PCs are built on basically the same chassis, and differences are located in particular story elements (eg what do bards look like in this game) and in somewhat marginal parts of the action resolution rules.
Although because I don't really know what's at stake in showing that a game is a new edition, or a revision, or a variant, I'm not really sure why these things matter as anything other than passing observations about resemblances among RPGs.