Fourth Edition Dungeons & Dragons implemented a more substantial change than any previous edition. Virtually everything was changed. It also sparked the greatest player split the game has ever seen. Everyone seems to either love it or hate it.
I certainly don’t want to revisit the “version wars” but it does beg the question: When a thing evolves, when does it stop being that thing and start being something else?
I would argue that 4th Edition Dungeons & Dragons is no longer Dungeons & Dragons. That’s not to say that it isn’t an enjoyable game system in its own right. But it is a new game system. It holds almost no resemblance to the original game. It has a new combat system, a new magic system, saves are different, the core character abilities (skills, feats and powers) didn’t exist in any form in the original game, races and classes only vaguely resemble their original predecessors, abilities (although named the same) are used entirely differently now, magical items are a commodity now instead of rare and mysterious items. Not only is it wholly different from the original, it has little in common with its most recent ancestor.
Instead of shelving 3.5 and bringing out 4e, I think they should have maintained both lines. Call 4e something else. Years (decades) ago they bought the game Dragonquest and shelved it. They could have used that name and produced products for both Dungeons & Dragons (3.5) and Dragonquest (4e). With Pathfinder, there would then be three distinct gaming paths and substantially more source material being developed for DMs to mix and match.