David Gerrold has also commented on the differences between the GR of '67 and the GR of '87.
The big difference between the two is that '67 GR was, as noted above, a working writer/producer who was just trying to find a way to tell the stories he wanted to tell and comment on the stuff that bugged him in a television environment that wasn't quite ready for that.
Also, he had Bob Justman, Gene Coon, Dorothy Fontana, et al to keep him honest.
By the time of TNG's development, writer/producer Gene Roddenberry had been beatified by the fans as "Gene the (mostly) Pius", so that even bringing Justman and Fontana back, with Gerrold as backup, wasn't enough to restrain the rampaging, and now slightly unhinged, ego. I suspect that even Roddenberry knew he wouldn't be able to keep the bit up for long, which was why he took Rick Berman under his wing (to head off another Herb Solow, network-spy-in-residence situation) and make sure that the person who took over would at least get the general concept right.
IIRC (and this is purely from memory) Gerrold stated (in one of his rant-ish responses to a Roddenberry bio) that Berman was not "hand picked" by Roddenberry. Gerrold stated that Berman was a studio guy who was put in place by Paramount to make sure that Roddenberry's trains ran on time. Gerrold also stated that Gene did not really like Berman on a personal level, either.
What hurt TNG, and nearly destroyed it, was the fact that Roddenberry allowed his lawyer (Maizlish) to run stuff, and piss off/alienate Fontanta, Gerrold, and Justman - amongst others I am sure. Only when Maizlish was shown the door, and a good writers room guy was put in, (Piller) that TNG took off.
This is the kind of dirty laundry that is and never will be part of the "official" Gene Roddenberry legacy, nor a part of the Paramount PR machine.
