You can try to put down TD's first season as much as you want (for those who do that), there is no denying that it IS great great television.
I've been a defender of season 2 from the beginning, keeping an open mind, knowing full well that it is somewhat silly to compare the two seasons, that people who did that were of course going to hate it, but I have to admit that the comparison is inevitable and season 2 is honestly not anywhere near the same level as the first, no matter how much I like it.
All the reasons have been given, what is annoying is to see Pizzaman being called a hack in some places, that Cary Joji Fukunaga made the first season what it was, but truth is, it's just a combination of elements.
Pizzaman makes True Detective what it is, but having a unified, coherent vision by one director on an entire series along with one writer is what makes the first season as great as it is.
Not to lack respect to the multiple directors of season 2, but with this season, we go back to the "writer is king" in a TV medium with Justin Lin establishing the look and tone of the series, but that guy's not anywhere near Fukunaga's level and then we got basically hired guns, the guys that direct episodes of GOT, or stuff like that, who just come in and do the job, nothing more, nothing less.
Season 1 had a much more cinematic and film like approach where it definitely seems and feels like Fukunaga had as much "power" and influence as he would have in the movie or film medium.
Season 2 doesn't have that, there was that rumor that Friedkin would come in and direct a few episodes, that didn't happen. Pizzaman also didn't have nearly as much time to write it as he did this one.
Add to that the diluted focus of having four characters instead of two, of having Vince Vaughn, who people are so used to seeing as a comedic, one note actor (I really like him but he has no range really, he does do what he does really well), saddled with corny, awkward lines every episode (another actor would definitely make it sound much better), a more conventional storyline, and you get something that's not nearly as interesting.
With that said, I really like season 2 but it's definitely heavily flawed, I love Taylor Kitsch but he has nothing to do with his character, I get why he was so excited to be part of the project, but his arc has literally no bearing on the story whatsoever, you could argue that Ani's character doesn't really as well though.
Colin is a clear MVP, he's great as expected, let's hope Pizzaman takes more time with the likely third season, gets a great up and coming director to come on board for the whole gig (I'm kind of dreaming of a Jeff Nichols-led TD season, or Derek Cianfrance, they would be great fits).