It is hard to do a proper critique without a frame counter but I will try
The first thing that stands out is that the steps are not of uniformed length “gate”, this is not a requirement but humans only vary there gate to avoid something which makes the walk look odd.
The spine does not seem to rotate as he walks, normally the hips rotate with the legs and the shoulders rotate with the arms causing a twisting back and forth as the character walks.
The feet are not properly planted on the ground, they seem to jiggly about a bit on the floor while they are weight barring.
The foot does not seem to roll, normally when you walk the foot lands on its heel then rolls until it takes off again with a flick of the toes. You can feel this by sitting in a chair with your feet flat on the ground, then try and lift your heel then knee as high as you can without using your thigh muscle.
Your animation also seems to lack fluidity in its moments. The speed of different parts of the walk speed up and then slow down. This is caused by incorrect spacing between your poses. If something happens too quickly increase the number of frames between poses, if its happening too slow remove a few frames between the poses.
Finally, you need to add some overlapping action and follow through. This means that you need to add movement that’s caused by other movement. For example the arms swing from front to back, but the elbows are connected to the shoulders so the rotation of the elbows will be caused by the rotation of the shoulders, meaning that there should be a small delay between what happens on the shoulders and what happens to the elbows. This can be continued down to the wrists and fingers as they are a chain of connected bones. But in reality this applies to the whole body.
Anyways hope that helped, awesome start and I love the character design.