Based on his
current form with Toulon he's almost definitely going to the World Cup and I can't really remember him ever having a dramatic dip in form over his career (aside from when he was played a couple dozen meters out of position at flyhalf).
There were some defensive lapses that were 50/50 him and the next defender in making mistakes or failing to communicate effectively in the last few tests before he got booted by The Coach but that's really all I can remember in that regard. In his larger test career he's generally been a very strong defender both in terms of positioning and the tackle itself, he has excellent tackling technique.
He used to have a bit of a habit of man-shaming international locks (I'm pretty sure he table-tops Victor Matfield later in that video as well):
(Having issues embedding with the time stamp but click to 1:15)
He's shown so far in Europe that his running game is still strong and has actually improved in the time between his arrival at London Irish and at Toulon (weather and pitch quality a possible factor) and he's gotten a bit better with his game management which makes him a stronger option at 15 than he was when he was younger.
O'Connor is still not, and should never be a 10. But that's fine because his footwork and acceleration is actually world-class, even if he is a little small in the 88-90kg range that still makes him about 10kg heavier and 10cm taller than Shane Williams (and arguably more skilled overall). As a red-blooded, god-fearing American myself I watch my share of NFL on Sundays and sometimes during the week and O'Connor is the only player outside of Folau who I think could absolutely switch codes and have a good shot at making a fist of it.
He's a freak athlete with a very broad but also deep skill set and if he can just keep his fucking head in he will be a huge asset on the field for the Reds and also Wallabies as he almost always has been in the past.