You've never played it?! Oh man, buy it immediately!
Yes, it is challenging, but there is a hero mode available at the start which maintains the same level of enemy aggression with a couple bonuses to keep you alive longer.
The controls are great, camera isn't bad in 16:9, and the game is just incredible. While very focused on action, the game actually ends up delivering just a wee bit of Metroid with its progression system. Once you reach the city, you'll spend the rest of the game moving around different locations using the city as a central hub. Places that you saw earlier can be accessed later often with changes. There are temples, a fire dungeon, ice dungeon, a monastery, and various other places to visit sometimes with light puzzle work (usually in the form of locating items and placing them in order to open up paths). It's simple but it gives the impression of a large adventure. With the absolutely incredible combat mixed in you're left with one hell of a game. Ninja Gaiden was, without a doubt, one of the very best games created for XBOX and is excellent on Vita.
I can't recommend it enough.