So it hasn't been about figuring out why 3E was "easier to get into". It's about refuting the assertion that 4E is obviously the most "not D&D" edition and therefore should be given the least amount of thought when designing 5E.
For the gamers that I, personally, know, 3e was considered closer. Much of this had to do with house rules that the various groups used and resembled 3e changes. Common house rules included
1. Humans multiclassing
2. Demi-human class and racial limits were ignored
3. Clerics and Wizards worked like spontaneous casters or the spell point system in PO: Spells and Magic
4. ascending AC was a common house rule
5. Ditching the Great Wheel cosmology (Edit:This was, actually, an example of something we did and wanted in 3e, but occurred in 4e and I want kept in 5e. I was being hurried to leave the house and put it here by mistake).
Three saves, monster ability scores, breaking down monster AC were things we wanted for a long time. It seemed logical, something we wanted to see, and grasped quickly.
4e seemed much different to us
1. The power system- especially for martial characters
2. Saving throws as duration
3. Removing ability penalties (especially, strength penalties for halflings and other races)
4. Overnight healing
5. a lot of the design philosophy in general
Edit: Despite my preference for 3e, there are several things that I would want to see from 4e. My preference for 5e would be based more in 3e, but there are many concepts I would bring in from 4e along with 2e approach to setting and campaign and 2e special priests.