The first 3 Dead or Alive games were decent. Dead or Alive Ultimate got lots of praise for including an online mode, but in terms of gameplay it was not really anything new, and in some ways was actually a step backwards for the series. Dead or Alive 4 recieved a very mixed reaction from series and genre fans, but in general people thought it was basically like Dead or Alive 3, but in HD and with some very stupid fanservice vehicle cutscenes. In all, it didn't really add very much new material to the mix other than new characters. Dead or Alive Volleyball 2 was just straight up crap, even moreso than the first one.
Ninja Gaiden was awesome (I own Sigma for PS3), but from what I hear, NG2 doesn't really do much differently from the first one, and ontop of that the camera is 10x worse due to the more demanding combat conditions. Also, the first Ninja Gaiden had a fairly stupid plot, and NG2's is apparently even worse. NG2 is still apparently a good game overall, but the reviews all seem to be saying one thing in common: it's not an improvement over the first one.
BTW, doesn't Itagaki look like he'd be the second-to-last guy who gets his arse kicked in a Jackie Chan movie?