As for the criticism, you asked, and I'm blunt. I'll try to not sound like a *beep*, but here we go-
Head shape- I started drawing with circle and oval-shaped heads, so I get why you draw it. It's easy and simple. But, it's not great in most art styles to try drawing someone's head circular. Leave YT animators out of this. Some artists do use circles to make different features, but it's more of a base. Head shapes in most styles are more or less similar to this-
Proportion and Anatomy- Your anatomy for the characters aren't bad, but could definitely use some work. If you don't know, the proportion is pretty much "the size of ____ in relation to ____". For example, the size of the head in relation to the rest of the body. You can usually fix this pretty easily by looking at references (always multiple) and yourself. One thing in your art, the head is the size of the torso. Now, that isn't necessarily bad as long as you mean to do it. For example, if you're drawing chibi characters, they typically have bigger heads than bodies, it's the style. But otherwise, the head needs to be a bit smaller. There are other proportional issues, but for the most part, it's fine.
Adventure-Time Noodle Limbs- The limbs and neck look similar to the limbs from adventure time, they look like thin noodles and have about as many bones as one. I've seen two successful artists draw limbs like that, and I really don't recommend it. It makes proportions harder, and it doesn't look great. And necks should never be the same width as an arm. Necks stem from the head. Look in the mirror, your neck doesn't turn into a pencil between your shoulders and head. I used to do the pencil necks as well, then I started fixing that slowly. It's not a good look.
Angles- You've drawn your picture in front-view 2D. The front view is used a lot, it's easy to do and it's actually one of the most common angles that portrait artists do. The thing is, when you are doing an action scene like this, you don't want a front-view. For a drawing of two people fighting, you want to try 3/4 view or side view. Now, I'll be honest, 3/4 view can be very difficult to learn and I haven't practiced side view much and I suck at it myself. With practice, it becomes easier. Plus, the 3/4 view (what I recommend) will help the image look more 3D.
Shoes/Feet- I don't have advice for this, I suck at drawing feet myself, but the shoes here look like hockey pucks.
Practice- One thing I recommend for practice only is tracing. Tracing things can help you get a good feel of how to draw something. Never claim anything you've traced as your own artwork, you get sued that way, but for practice at least, it can help more than you think.
These are some websites I recommend if you want some references and tutorials.
Art for Kids Hub