Thank uou, now I understand completely ^^
The trick you suggested, using a videocamera or a mirror is very useful, and I'll probabily use it in the future to understand better what to do.
To tell the truth I though I had done a fairly good job with proportions (well.. better than usual, let's say XD), but well, that's why we need critiques, right? Anyway you're right about the other thing, the change of lenght of the weapon and the expression that looks strange in the foolowing frames. It's probability because I concentrated more on the "action" than the details, but I understand that everything is important in this sort of things. So I'll assure you that I'll put more effort in every detail. Maybe I'll post the rouhly skecth in the WIP section first, next time, so I can correct the mistakes before it becomes more difficoult :)
Thank you again for taking time to explain me, It really helped ^^ and sorr if I sounded dumb XD

volumes, particularly in the upper body, change in every frame.  The spine compresses, the head changes size and shape, and the well proportioned body from the first frame becomes unrecognizable by the time she (attacks?).  The face, which also begins well constructed, degenerates into a shapeless mass with an overgeneralized expression - the type seen in poorly drawn anime.  The handle of the weapon changes length in any number of ways.

When animating, it isn't actually good enough to pay much attention, you need to actually go through and sight and measure and make sure that nothing changes in its perceived size unless it should.  100% isn't a goal, it's par for the course, otherwise everything looks broken.  Animation of humans with realistic proportions can't be a squashing effort, or even if it is, the forms need to remain fairly consistent in the ways they are squashed.  When you go through each frame, the girl should have the same body type, same proportions, and same general construction, simply moved, angled, viewed differently.

I also would get yourself in front of a mirror or videocamera and perform this motion so that you have a direct reference to the way the human body moves in this situation.  You'll find that when everything maintains it's structure, the way that it moves is much more complex and at the same time much more beautiful.  Take into account balance, anticipation, flow, and strength (right now the thrust, if it is a thrust, has no power because of the way it's timed,  try and figure out a way (if you don't know just ask) to put a little more spike in her strike.

Umh, ok, I know it's not perfect at all, and Iì've never hid the fact that I'm still learning and that's why I've posted this here, because I want to learn.
But I think your critique is.. harsh with no reason to be o_O Anime trash expression? What does that mean? Look, I accept critiques. I had lots of useful critiques to this piece, And I'll surely remember every single one of them for the next piece. But yours doesn't add anything. Confused perspective? You are maybe right, but could you tell me *extactly* where? SO i can understand. *Massive* shifts in size and weight? Sorry but I disagree, because I paid much attention to make everything even, and i think I managed to do at least that. Maybe not at 100%, that's right, but i said it's far away from perfection. And I'll pay even much more attention next time.
Sorry If i sound a crybaby or rude, but i wanted to be clear, don't take it as a flame, but as a discussion.

wawawa confused perspective, massive shifts in sizes and weights, anime-trash expression in the second part.....why bring these things into what was a rather nice piece with just the basic frame of her standing?

this is pretty sweet :D

Thank you everyone for your critiques, now this was a gift so I won't retouch it anymore, but i'll *surely* remember your useful advices for the future, thank you ^^ This was my first serious animations, so I still have a lot to learn :D

I will agree with the rest... Animationis wierd, but I like the drawings a lot.

Small picture look like sex XD

although it has 23 frames, it doesn't look completely smooth... it also appears that the last part only has 2 different frames... 3 different frames may already have been a huge difference... and at frame 10 and 11 (the moment she turns around) it looks almost like theres a frame missing... and i agree with migoy, the breathing is a bit weird... too fast imo...

But well... enough about the animation... if i look at the frames themselves it looks very nice, although i would have made the legs a bit longer (especially the shin)... nevertheless a very nice piece! keep it up

sorry for being stupid, but the preview looks kinda *weird* :-)

I like what you've done but I can't help but think it would work a LOT better a quater of the size. I don't think a "profesional" sprite this large would be done in pixel art. Try starting smaller if you want more practice at serious animation :)

her breathing's kinda weird,and there are lost white pixels on the staff anyway nice pixel for a start.