While I agree Both Ninja Gaiden Black and Ninja Gaiden 2 are superior to Sigma, I love Sigma too, there's a wider gap between Sigma 1 and Sigma 2 for me in quality compared to those.
Sigma at the time was great in the early days of the PS3, had to order a US copy of the game since it the only version that was not censored, it was interesting seeing a remake that early since the original, that also got a Black version, I had both original games for Xbox, so for me it was more stuff added, albeit some of the added content was dividing among fans, Rachel sections being mandatory for one, and offered the opportunity to Playstation users to experience that awesome game.
Sigma 2 is a travesty, no gore, fewest ennemies on screen at the same time for technical reasons completely ruined the game pacing and intensity of the encounters, you trade all that for a few neat additions, mainly new bosses and other characters playable in separates chapters, but the core of the game, 90% of the time you spend playing the rest of the game is fundamentally a downgrade.
Ninja Gaiden 3 is baffling, I didn't bothered with the vanilla version and went straight to Razor Edge months later, the problems for me are the story, the gameplay design ditching the essence mechanics and the weird steel on bone gimmick, bad bosses, but on the other hand the combo system and moveset is just incredibly deep, the gore is awesome, that I would savaged for a NG4 without a doubt.
On the recent compilation, we had the bare minimum and at this point I'm just glad the franchise don't collect dust and the more you let new players experience NG helps keep the series alive.
