What hasn't been pointed out in this thread is that both TOS and TNG aired during a time on tv that procedural shows were the norm and only cheap weekly soap operas, that were looked down upon, did serialization. That's why that being episodic is never held against TOS and TNG.
But Voyager and the first two seasons of Enterprise followed directly after DS9, which focused very much on serialization, feeling like a let down since they went back to the episodic format. TV had changed around them but they refused to do the same. That's a big reason why ENT's ratings fell and that show ended up getting cancelled.