Ng3 Razor's edge is also a good game, but almost every aspect is worse than the previous titles. Worth playing.
Razor's edge is good, but NG3 original is an aberration.
It's quite a feat they managed to make razors edge out of it.
I've never even heard of Razor's Edge. It looks like they just facelifted NG2's engine into the NG3 campaign? A quick glance and all the sounds/animations are identical and it seems to use the same i-frame/execution/resource system.
Razor's edge is an updated version of Niunja Gaiden 3. They popamolified Ninja Gaiden 3 (made the game for casuals, with a lot of QTE, a bit of stealth gameplay, lots of cutscenes telling a lame story that tries hard to be like a metal gear), and everyone hated it. Razor's edge just revamped the combat system to be just like NG1/B/Sigma and NG2/sigma - and remove most of the QTE and stealth, and what couldn't be removed due to scripted sequences were made less boring and more forgiving control-wise. But the linear levels are still the same (and the lame story), so it's limited by that. But Razor's edge at least feels like a Ninja Gaiden Game. They even manage to put scarabs and skulls, but the linearity of the levels make them kind of easy to find. There's a lot of hidden challenges, one in each chapter (you have to find the skulls), where you have to survive waves of enemies, and face bosses from the whole series, brought back for this game. Razor's edge is kind of the Sigma version of NG3, only it was totally incline this time.
The only thing they maintained from NG is the health/Ninpo system: You start each level with a big health bar, and builds the ninpo bar by killing enemies and stacking combos. You can only use ninpo with the ninpo bar filled, and you have two choices: Refill your health, or use the ninpo. Health is one thing that will piss of casuals though: If you die, you restart at a checkpoint with minimal health, and the only way to recover it is by building ninpo. So, if you die before a boss, you start imediatelly before the boss fight, but with a very low HP. Oh, health restore to its fullest when you meet the save point. There's checkpoints in between, but you have to go with the low health, and sometimes, the next savepoint is after the boss.
For more detailed info on the series, check HG101:
http://www.hardcoregaming101.net/series/ninja-gaiden/
http://www.hardcoregaming101.net/ninja-gaiden-3-2012/
Oh, and a comparison of performance of NG2 and Sigma. The should port at least NG2 instead of NG2 sigma.