I tend to think the people around him -- Justman, Fontana, Gerrold -- were as much responsible or even more so for TNG having any chance. These were people who actually co-created TNG but were robbed of getting any of the credit by Roddenberry's massive ego. If it hadn't been for them, TNG may have been DOA.I think the fact that Roddenberry was going a bit loopy when he made TNG made the show much better
Making it fresh and different was the way to go, if they had gone with a different producer we would have ended up with a ripoff of TOS instead. He took a big risk because he believed 100% in his abilities and believed in his concept while all around him producers were stating he show would undoubtedly fail.
Without the foundations that Roddenberry laid I think the second Trek series would have not been as successful. It is fortunate that people were able to build upon his work as he became more ill and made the show better.
Roddenberry was in charge though so he should get the credit IMO because if it failed and was DOA you can bet he would've got the blame. He came up with the concept and the characters etc I think? He had some lame ideas but some good ones too. Berman refined it later on. Sure the people around him and Berman were a huge part of the success but Roddenberry came up with it! He assembled the team?