That 3Ed was as radical a change from 2Ed as 4Ed was from 3Ed I find to be non-controversial.
The differences between the transitions, though, are crucial:
1) WotC tried to make it possible to transition 2Ed PCs and campaigns into 3Ed campaigns with as little pain as possible, even going so far as to publishing a conversion manual (of which I own 2). With 4Ed, we were told conversions were essentially a waste of time, and that starting anew would be preferable. This means that those of us who had campaigns dating back many years (like mine which started in the 1980s) were essentially given a date certain after which those campaigns would no longer be supported by the new version of the game.
2) 3Ed changes were largely mechanical, not fluff, and the mechanical changes were, by and large significantly positive changes to the earlier editions. The math, for instance, became much more intuitive.
3Ed didn't touch the fluff by excising classes or races. It didn't alter the cosmology significantly. Instead, it was about expanding possibilities- hence, the elvish paladins and more open multiclassing structure.
In contrast, the mechanical differences weren't inherently superior, just different. Racial or Class options that existed in the 3Ed PHB were gone. The alignment system was truncated (and in an oddly unbalanced fashion).
3) 3Ed was all about freeing up character options. Within a small set of restrictions, you could have your PC of any race have any combination of any classes...even if it was mechanically sub-optimal. The designers of 3Ed trusted the DMs and players to be able to design fun PCs and campaigns.
4Ed's design favoring a mechanical preference for balance is inherently more restrictive. A sub-optimal PC is much less possible. The 4Ed designers tightening of PC design restrictions (especially in multiclassing) amounts to a lack of trust in player decisions.
IOW, whereas in the 3Ed transition, WotC tried to ensure backwards compatibility, maintained many thematic touchstones of the game's previous incarnations, and expanded options within the Core releases as compared to its predecessor, 4Ed was decidedly NOT backwards compatible, killed or maimed many sacred cows, and reduced Core options as compared to 3Ed.
Obviously, that didn't sit well for many.