This is the first NES/Famicom game I have ever completed - and what a fantastic game it is. While my eyes boggled at the bizarre colours and backgrounds, the incredibly fluid and fast gameplay, excellent controls, great music, awesome cutscenes, and just all-round badass-ness of Ninja Ryukenden had me hooked right from the start. I even love Ryu's "only my legs are animated" run, it just suits the game so well.
Sure, the game is pretty relentless and brutal, but it's not actually that hard to come up with strategies to get you through the rooms. By far the biggest stumbling block is the penultimate end-boss fight, the Jacquio, but rather than the fight itself being insanely tricky, this is more due to the massive setback of being thrown right back to the start of 6-1 and having to trudge through all the hardest levels again before getting a rematch. Full disclosure, I had to switch to an emulator to get to the Jacquio fight so I could get a save state and actually learn the fight. It probably would have taken me months to get past him on the native hardware alone, but now I feel I have a decent idea on what to do after only a half-hour or so of rematches.
What really surprised me was how little frustration I felt while playing. Even when the simplest mistakes cost me lives over and over, I simply enjoyed playing so much I was laughing rather than swearing. I haven't felt quite so rewarded from a non-competitive video game for quite some time.
I look forward to many more playthroughs, and also the sequels.