A few tips
Invest into frame by frame. working on so many body movements
Also, katanas are used in both hands ^_^ generally a lot of the things here you said about ninjas is generally incorrect ;P know your stuff ;p
Besides that, yeah, the two weeks really show - the animation is largely unpolished in terms of smoothness or backgrounds.
But hey, don't let that get you down ;) I think that animation made you improve by a ton and can't wait to see the next one ;)