I think it's mainly the acting. It is difficult to think of a TV actor more annoying than Michael Weatherly ("DiNozzo"): yeah, everyone has the right to be stupid; but to brandish that light-weight stupidity around is, well, unethical..."Gibbs" ? He has two expressions that he keep using with emphatic effect, which gets rather tiresome: stare; tilt his attention sideways. Great. Fire your acting coach.
On the other hand, one should perhaps be more charitable: with tasteless, wooden lines given to the cast, what can you do? So,the screen-writers are no less culpable.
But the plot is silly, too---wait, wait, "Criminal Minds" has its fair share of lousy stories, too; it is probably just more obvious in "NCIS", because of the super-lousy editing, and the worst cinematography of any TV drama in recent memory.
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