I am not a huge fan of the new one either, but let's remember that the audiences that grew up on the original Indy also grew up. We live in a much more jaded society, where everything has to either be deemed a success or failure within minutes of its release (sometimes even before).
Also, movie making technology and the spectacle of the summer blockbuster has been amped to the Nth degree since the original three films. Audiences keep expecting to be wowed by bigger set pieces, special effects, etc. It is hard for filmmakers to come up with something new and exciting it results in more spectacular failures.
I tend to agree with Lucas that we tend to put things from our childhood on a pedestal. That does not mean that I think the TPM or IJatKotCS were necessarily good, but I do think that RotS was better than a lot of people give it credit for.
If the original SW came out today, it would be picked apart by mass media and internet social forums within minutes of its release. I don't think it would have survived in today's instant success or failure marketplace. The original resonated with audiences because there was nothing like it and it had no competition. Today it would be in the theater for 2-3weeks before the next big release and the audiences attention would be devoted to something else rather quickly.