Cousins has been good but I need to see much more of a sample size out of him before I think he's anything more than an Alex Smith, Ryan Tannehill, Andy Dalton, etc.
His completion % is through the roof because the vast majority of his throws are within 5-10 yards of the LOS, he doesn't really attack the intermediate areas it seems, his throws are either short dump offs or relatively safe bombs along the sidelines, of course with one of the better deep threats in the league. I can't say this for sure because it's not like I watch every single NFL game but it seems that he has had an inordinate amount of short passes taken long distances this year. I think he has had 2 or 3 screens taken 50-60+ yards this year, I can't really remember the Cowboys having a screen hit that type of gain in the last 10 years honestly.
Most of his production has come in the 2nd half of the year against some of the worst pass defenses in the league (Philly, Saints, Buffalo, etc.). I think he's a solid QB, a guy who can keep you competitive and who you can win with if you have a strong team around him but the fact of the matter is that they are only 9-7 in the worst division in football and they haven't beaten a team above .500. Of course once they give him 18-20 million a year after this season that will seriously inhibit their ability to build around him.
Even the Packers have been playing poor for damn near 2 months now, if they were to beat the Seahawks, Cardinals or Panthers then I'd be really impressed.
Basically, the guy has had like 4 or 5 huge games this year where has thrown about 16 or 17 TD's to 0 INT's, the majority of those games coming against horrendous defenses or teams that had basically quit at the end of the year. Aside from that his TD:INT ratio is more or less 1:1 because they run a very conservative offense with passes that are designed to be high percentage, low risk plays.