Well... this is my second night with the game and I want to touch on a few things I have noticed in playing with actual people today. Im going to go through a list of attacks that have proven useful and will go over some things that are good/not so good. Overall Ill say Natsu is a really competitive character when compared against what little I knew of Taki in SC4.
a4 - (a) punishable on block. decent dmg for JF (42) spacing on hit allows for followup/mix up 6+b+k and b+k.
a,a - Safe on block I tested this against Leixia standing A which i assume to be pretty quick.
a,a 4 (feint) - Places Netsu in full crouch allowing her to do any WR moves and buffer into throw attempt (I recommend 66 B+G).
a,a,b - 5 hits only NC on CH. You can not hit confirm this string but the whole string seems to not be launch punishable at all with a fair amount of push back on block keeping you at a nice distance ( about 2 character spaces away).
6+a, b(k) - string a,b version is not a NC unless CH. I use this only to set up 6+a, k which knocks down right in front and can set up 2,a+b (ublk).
I have to go but ill be back with more stuff. Thanks for your patience.