Legit opinion. I find the second half being like that, and I've seen many hold the same opinion. If you care, I tried to remember it and highlight some points.

• Solid art direction and big animation budget (was it Madhouse studio?);
• Like many media, they are selling two characters-stereotypes and their dynamic - hard-disciplined OCD narcissist and his complete opposite (that's why after one dies show loses my interest), both looked different to what average movies do;
• Writers took a couple of twists about how Light creatively secures himself and kills people with notes and they are fun to see as much as Sherlock's explanations of his logic solving a crime;

But what I want to single out: it was made for teenagers and young adults. Confusion about their lives, wish for some superpower or direction, being able to overturn the frustration of their first boring work. With a shade of phylosophical themes that make them feel like it makes them clever, with guessing what if they end up in the same position, with bleeding edginess of deaths, god complex, acts that can be rightfully called terrorism (plus it's geeky and cool if you watched it when anime wasn't mainstream at your place - it's a kind of a community, and for some - their personality trait). If you don't consume a lot of media and DN became your first anime somewhere between 12 and 22, you'd probably like it.

And it usually kills it when you leave this age group, don't like edginess, fog of intelectualism, not only ill but just immature characters, everything turning around them and don't feel like watching episodes just to see these characters' tricks and quirks. And what can come from psychotyping (yeah, this geeky horoscope) there's no emotional information coded into the series, just pure 'we see these smart men outsmarting each other' and rotating the rules of Death Note like a rubik's cube that is problematic to many people - I'm the opposite, I don't find relationship drama even IRL interesting, but I understand the opposite can be as empty on the other end.

So, as all media, it's a matter of taste and background.