the beauty of the NFL is that you can never get enough. You make the season two games longer and people will start to "get enough" so to speak.
As it is, you have the draft, then rookie camp, summer OTA's, four pre-season games, the regular season and four weeks of playoffs. So, you have 26 weeks of actual football counting the pre-season. You're looking at half the year anyway and the half of the year that there is very little football news has ALL OF US clamoring, begging for it (and hoping none of our beloved Steelers does anything dumb).
I think they should do a better job of putting together a developmental league of some sort, for smaller markets, like minor league baseball. Most minor league baseball players never sniff the big leagues, most minor league football players wouldn't either. But if they could be called up for a game or two b/c of injury, etc it could be a good thing. Or they could expand the rosters a bit.
But I digress, 18 games is too many. The Market for the NFL as of right now is about as good as it gets IMHO.