I think the Sigma games can best be described as me remaking Chaos Legion for another console. I kind of know how games work and what makes a good game, but I have zero relevant experience with the game in question and a tight deadline to boot.
The Sigma games are great in that they build off of a phenomenal base set of games. But everything they add or change is either a result of not knowing how the game actually worked or general oversights.
Taking Sigma 1, they changed the back-dodge animation. Which sounds fine, but it royally screwed up some elements of the game. Certain sections of calm are now filled with enemies, screwing with the pacing while other short fights now have waves of 20 enemies total.
It goes further than that too. The timers per fight are not adjusted for the higher enemy count, making some timers impossible to complete, showing that lack of attention to detail. Similar details are missing in weapons, smoke bombs barely work now for whatever reason, Incendiary Shurikens now bounce off of some bosses instead of damaging them, enemies that were a menace now have all their attacks be parryable etc. Details details details. They won't bother someone doing a regular romp on Normal difficulty, but for series veterans the game really missed a lot.
The only things I feel are improved are the fact that you can unlock higher settings faster by beating a (boring) optional boss. That and they removed all the puzzles. While I don't really like that latter part I can see players who played NG:B for years on end feel good that they can now just skip all the busywork and go straight to the combat.
Sigma 2 is just a bunch of quick fixes going absolutely out of hand. The big problem with NGII originally was its frame-rate, which they fixed by lowering the enemy count in Sigma 2. But then to balance this they...gave enemies a huge health boost. And to balance this they lowered delimb-chances. And to streamline the game further they removed the currency system. And to balance that... and it just keeps on going from there. That game is so far away from the original I consider it a totally different experience, though I still prefer NGII's original vision.