No, The Next Generation should have been the series that fleshed out the Romulans. They were featured quite extensively and we learned next to nothing about them. It was a missed opportunity, and after that it was too late.ENT could've, and should've been the series that fleshed out the Romulans, but failed to do so.
Well, I'm not sure I agree with that. Don't get me wrong, it would've been great to get the Romulans more fleshed out. But I think TNG originally intended not to revisit a lot of the TOS races and that's why we got the Ferengi and the Borg. Also, TNG seemed more intent of fleshing out the Klingons.
I think ENT was a good spot to flesh out the Romulans since the other series hadn't, plus it was in the time period of the Romulan War, which made it the best candidate to flesh out the Romulans. In both TOS and TNG, the Romulans were emerging from long periods of exile. But in ENT timeframe there were no such restrictions.
