Input delay was a huge problem thanks to the framerate in 3 and that was especially true at higher difficulties. On Normal it played like a perfectly sound action game. Higher than that, and especially on MN, it became nearly unplayable. The final fight on Master Ninja nearly broke my will to finish it and I haven't missed beating a single core release (NG/Black, NG2, NG

S, and NG3) on MN at all. I didn't finish any of the Sigma's on MN because for whatever reason I lost interest.
Let's be real, though: Hayabusa has ALWAYS had problems with targeting the wrong enemy and that's not unique to 3. Wasn't even any worse.
Razor's Edge has me genuinely excited because it's going to be a significantly better game than 3 by default; we may even enjoy the parts of 3 that bothered us in its first iteration with some fancy new distractions. I personally hated the fact that we were basically walking down a path into what amounted to a wave-based arena battle and repeating it throughout the whole game. While there were other issues, that just seemed way more painful than in any other title because there was so little else going on.
We had one weapon, little enemy variation, one Ninpo, some seriously flawed AI for enemies, grabs becoming the new IS spam, no health bars on bosses, and a narrative that never got broken up by something fresh in the gameplay. We now have several weapons and the ability to purchase skills and upgrades, new enemy patterns (not sure if there are new enemies but I don't recall any in the Wii U version), several returning Ninpo, interruptable grabs if you're on point, health bars, Ayane missions, and the addition of Kasumi and Momiji during Shadows of the World (if the MP component is still called that). There's more but I'm distilling it down to major bullet points.
I think this game has a shot at bringing a lot of us that felt let down back into the fold and, at a discounted price, it feels like a nice gesture from Team NINJA. The way I see it our purchase here shows TK and Team NINJA that we are interested in paying for an improved Ninja Gaiden. We are interested in putting up our money to keep experiencing the Team NINJA brand of action. And we are definitely interested in supporting trying new things as long as it pans out. NG3 was obviously an experiment on many levels and a good majority of us rejected it after playing the finished project. Instead of scrapping it and focuses on a new title that is really just more of the last successful title, they said "No, we can make this better," and seemingly did so. The critics definitely bought into it and nearly unanimously declared Razor's Edge a vast improvement over 3 and worth of the name Ninja Gaiden.
It's about time the Master Ninja fans got their hands on it and weighed in...and without using that gaudy fucking Wii U Gamepad.
...and yes, that totally came off as a bit preachy, but I'm extremely passionate about this franchise in case you didn't figure it out yet!