I absolutely love this game! It's a blast to play! I hardly noticed a single one of the glitches you mentioned in the post with the download. I'm gonna break this analysis down so I can give better feedback.
Glitches
There were not many glitches that occurred while I played. There were only two very noticeable glitches during my playtime and each can probably be fixed with ease.
1.) During the first level I ran up on a seam in the ground. The enemies fell through the seam and constantly slashed at nothing in the background. They were obviously out of the level, but I could still hear them hacking away. Just close up the seam and you should be fine.
2.) After I died (I died numerous times), if I waited for around 15 seconds, my character would come back to life, spewing blood. He was fully controllable but died with a single hit. The "You died, hit return." screen was still there, as well. That's all that I encountered glitch-wise, fortunately.
Annoyances
1.) I have no return button. There just isn't one on my keyboard. After I die, then I have to bring up the start menu and click play. Which doesn't seem natural... Perhaps make it the enter button or backspace?
2.) I would like to see some difficulty levels. I honestly had some trouble with the enemies. I died a good ten times and I only made it to the end of level 2 (Which was awesome, by the way). Make it to where they do less damage on easy, a little bit more damage on medium, etc.. This would make for an interesting game on Ninja mode (like an impossible mode for the hardcore players.)
3.) I was disappointed you took out the speech bubbles. It broke my heart. Try and find some time to put them in, Mkay?
4.) No aerial attacks. I could definitely have used some aerial attacks in quite a few situations, and I think it would make for an interesting addition to the game. Try and squeeze these in there, also, because the game seems lacking because of it.
5.) I didn't get a good explanation of the attacks I could use, in-game. I still don't know which button out of ZXC is high attacks. This isn't a big deal, though, because I didn't really care what attack I was using when slashing through evil-ninja-faces.
Likes
1.) The Platforming. I think it is awesome. I love it. I enjoyed it, and I think it added a good level of difficulty to the game without being too hard.
2.) Holding the down-arrow to show when to strike for a 1HKO was brilliantly designed. I thoroughly enjoyed slicing the bad guys completely in half. Awesome feature.
3.) The movement was well done, as well as the acceleration.
4.) The atmosphere was perfect. The music fit great and the clean stylized graphics were wonderful. I liked the way each level differed from one another with their own color theme.
5.) Chi-mode was definitely very cool. I had some fun with it, but didn't use it as much as I should have because I forgot it was there sometimes. But still, very cool feature.
6.) I had a great FPS when playing the game. No lag at all, and I have a crappy integrated card... I'm so glad that it worked as well as it did.
Suggestions
1.) Bosses. Definitely try to get some end-level bosses in there. I think this game seems to be begging for a few gigantic bad-ass bosses. Even some human-sized ninja-like bosses would be cool. Probably sounds corny, but I think it'd be a great addition.
2.) Power-ups should be added and hidden throughout the level in hard to reach places. Temporary health add-ons, insta-kill for 30 seconds, jump boost, chi refill, health refill, power boost, speed increase, etc.. Basically, all of the usual stuff.
3.) Speech bubbles, of course.
4.) Change the death screen so that it asks for a key other than return.
5.) Fix the few glitches that you have.
6.) Aerial attacks.
7.) And lastly, I suggest that you get this baby finished!
Further Comments
I had a great time playing, and I cannot wait to see the future features you plan to implement in the game. I loved the demo and I expect to see this game becoming very popular here on TGC. Hope you find my post useful, and please remember, I'm only trying to help so don't take any of the negative things the wrong way! You're an inspiration to many of the coders on the forums here. Congrats on getting the demo out.
-HC