ST:TNG worked better specifically because it was not serialized for the most part,
Nice try, but ST:TNG wasn't serialized because it wasn't something that was done at the time. When ST:TNG came out, sci-fi shows were simply not heavily serialized. X-files had a little bit, but only a little bit, and that was it.
TNG was part of the evolution in scifi shows in that it introduced more and more two-part episodes, which were OMG almost like having a movie! Serialization was much more of a product of Babylon 5, where JMS wanted to tell a particular story. DS9 grew in part in response to that competition--you not only had larger story arcs, but you also had more aliens, ship shots, more everything. (Except for how they shot a war with around a half-dozen actors.)
There was an explanation for O'Hare leaving, btw, that was planned in advance, although I agree it would have been better to keep him. JMS planned an exit strategy for every major character in case they left the show before the story was through. That being said, the fourth/fifth season thing sucked.