Did anyone here play the sequel? Is it any good?
Yes, the sequel to Ninja Gaiden, Ninja Gaiden II: The Dark Sword of Chaos is awesome. The most obvious improvement is the fact you can scale walls easier (think Spiderman) and you can increase you maximum ninja power by collecting scrolls hidden in each stage. Outside that the story and characters rock and the cinematic style of the first game is continued. Basically, if you liked the first game I don't what would stop you from enjoying The Dark Sword of Chaos – if not more.
However, I was pretty disappointed with Ninja Gaiden III: The Ancient Ship of Doom. It just seemed pretty lackluster even with its improvements (more animation and new weaponry.) Unfortunately, there was a bug in the original NES game that made you take double damage from everything (it was fixed in the SNES compilation NG Trilogy) so you died 2 times quicker than you should have, it makes it pain to beat it.
I wouldn’t hesitate to purchase the first or second Ninja Gaiden games on any of the console’s online stores.