To those underwhelmed...
Just think about this way. You have directors like Tarantino that often bring out the best in actors. (If you don't like him then whatever you get the point I'm making). Basically, sometimes the right director + right script, can really bring out an incredible performance from an actor you might not be all that fond of.
I know a lot of people didn't like Matthew McConaughey for many years (with good reason). And yeah, well he's actually had great roles prior to True Detective, I bet you anything if he was picked to play this second season role before Dallas Buyers Club, most would have groaned. Thing is, True Detective was a new show. So my point is, people now have expectations due to the high caliber placing the show has put itself in. Had True Detective been this good without Matthew and he was cast prior to Dallas, I really think that people would have been disappointed too.
I'm willing to give this a shot, because I think if the writing is strong enough, and the directing is great...I think Colin could pull off a great performance in his own way. Nothing will ever match Marty or Cohle. And nothing should. It should be its own thing.