Alright, I have been playing this game for less than 24 hours but I have spent much of that time with Nariko. First, I am a huge fan of fighting games and I primarily play SoulCalibur V. I wanted to play this game and when I heard that the combo system had some depth to it, well, I just had to try it out.
My first impressions of Nariko are mixed. In a 1vs1 match, Nariko is extremely powerful. She can easily do combo strings that nab her a TON of AP. For example, Down Circle, Circle, Up Triangle, Up Triangle (air), Circle, Square, Square, Square will gain Nariko 150AP. That is an instant level 1 super! Her combos look beautiful.
Stuns are a very strong part of her game. They are necessary for her combos. Her staples are her circle moves. Down Circle, Circle, and their "Air" variants are important moves that allow you to follow up with many of her other moves such as launchers which, in turn, allow you to follow up even further.
Nariko is a close range fighter. She has some projectiles, but they are no where near the league of Radec's sniper rifle. They also gain her very little AP. She is best suited right up in the face of her opponents. Her Down Triangle moves even grab your opponent from a distance and drags them to her Scorpion style. It is best to note that her Down Triangle on the ground is infinitely better than her "Air" version, allowing for more significant follow-ups. Too bad these moves don't track like Kratos' Forward Square.
Anywho, these strengths become severe weaknesses when playing a 4 player FFA. Her combos are geared towards single targets, so she becomes vulnerable to other opponents thusly. Also, her combos are lengthy, leaving her a sitting duck for far too long. I found myself constantly interrupted or otherwise dropping my combos just to avoid getting hit by everyone else. And because she needs those combos to build her meter, she can have a hard time getting to her stronger supers. It becomes a bigger hindrance when you have to be right in the action to be effective. The best strategy is to weed out the runt and avoid the pack.
As for her supers, I have not yet found a combo that would guarantee a level 1 super. Her level 1 super is not that great. It's better than a lot of others, but you would still be hard pressed to make good use of it. At first, I thought it was awesome, I got that "Three for One" trophy easily with it. I was getting 2 kills with it often, but shortly after, I actually found it to miss alot. Nariko's level 3 super is her best super. You can easily get 6 to 7 kills with it. And that is usually enough to win you the match. Though, you really need to remember which attack do what to make the most of it.
So those are my first impressions of Nariko. I have played a little bit of Kratos and I gotta' say, he seems to me a stronger character. He gains good meter with minimal effort, has a lot of knockdown and pushback moves, and (save for his level 3) has superior supers. If I were to compare these two characters to characters from SoulCalibur, I'd have to say Kratos is like Mitsurugi and Nariko is more like Viola. Kratos has those effective quick pokes and Nariko has those impressive, lengthy combos. The former being far more effective in a 3-4 player environment.