Hi there! What do you think? I've just learned the basic of Sfm and i'd like to know how are these animations :)

Your core motions are pretty decent, however it looks like Shepard does not have an iK rig in the first animation, you should find or make one as soon as you can. Otherwise, I would suggest you work on adding more detail to the animation, such as subtle nuances in non-central extremities. This is fairly important for looping gifs, since your animation is only a few seconds long, you can afford the time on attention to detail. Still, great start!