I remember reading about the show when it premiered and they discussed where the characters would go. Data was supposed to be a Pinocchio and Wesley Crusher was intended to be an important character. The casting didn't help there --Wheaton was simply too dull for that. Jonathan Brandis had a similar role in Seaquest and he was ok (although he had a dolphin co-star). Wesley Crusher became the JarJar of Star Trek and not for anything he did, just the fact that he was so uninteresting. There was one episode where he was given the major focus and his co-star was Ashley Judd. I remember thinking that she could go places because she stood out.I think that the focus on Data in so many episodes did not help the flow of the series. There seem to be a number of episodes with interesting sub-plots that are partly spoilt by trying to shoehorn in a personal storyline for one of the crew (usually Data or Wesley).
Riker was intended to be the man of action--he was supposed to be doing all the Away team stuff and they sidelined him pretty fast.
Then there's Deanna Troi reading everyone's minds.