NGB was awesome, but had more open levels and backtracking. I remember Alma just being hard as hell, well most boss fights being hard as hell. Some puzzles rubbed me the wrong way (pyramid anyone?). Otherwise stellar.
NG2 action-wise is insane. Is it a better game? That's up for debate as the 2nd half of the game really seems like filler. The Flying Fortress Daedalus level may perhaps be my favourite NG level ever.
NG3 was pretty bad for a Ninja Gaiden game, but a pretty good action game. I really enjoyed the boss fights in this game.
NG3:RE is a huge improvement, but a strange one as they modified the combat engine to me more like NG2. You can play all 3 characters completely through the game though.
Yaiba.... Wrapped this one, but again hard and not in a good way. Platforming was strange. Boss fight with Ryu was so cheap. End boss drove me nuts.
O.K. make all this BC on XBOX One plz...