well, let's say you would like instead to animate a jump. There are two way you can bring in animation: create a new picture for the next frame, or keep the previous picture, but move it around. I think AdamAtomic's point here is that you will get something much more interesting by using only a few distinct pictures that show dynamic poses that keep the spine of your character rigid during the whole jump but have a distinct legs position that shows a very smooth movement of the legs while the rest of the body is barely affected by the move.
Yes, you made good-looking pictures and a smooth animation, but from an animator's point of view, your animation is flawed because you do not take into account masses, inertia, pivot feet, weight placement and things alike. And the reason it is flawed comes from the very technique you've been using for animating it.
i don't have pictures of someone using a katana right now, but i feel if i was to hit someone hard with that kind of weapon, i'd be "charging" my musular energy and then "unleash" it just like if i was striking with a baseball bat. So here come some kick baseball images:
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->
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Okay, the move is not exactly the same, but note the "idle-charge-unleash-decay" process. Note too, how much the shoulders and hip lines are involved in the process. If you do the move yourself, you'll feel how your weight is transfered on your back foot and then back to your front foot in the process, and that's an important thing to show in an anim to get some "realistic" feeling (imho).
I perfectly understand your process though (or at least i think i do, because i did the same with ulgier results): you're kinda proud of your initial (still) picture of the character and you'd like to see him animated, though you had hard time coming with that level of detail and you fear you cannot redo the same level on +16 distinct frames.
This is exactly why the process of animating by drawing fresh frames suggests that you stick to very simple shapes until you've got a convincing move, and *then* progressively bring back details.
(now, that being said, i still suck at drawing people and wouldn't be able to come with a decent sword animation without tons of practice and sketches)