Normally, with a character model you just make one half of the model then mirror it over and weld both halves together. That way, both sides of the model would look the same, as opposed to the uneven look it now has.
Lets see... The face looks like its collapsed in the center, gives it an odd appearance. And the head itself is too rectangular in shape. He has absolutely no shoulder, you just attached his arms straight to his torso.
This is how shoulders should be done (yes I know the site has a weird name, but I assure you it is most definitely a real site and there's nothing inappropriate on it). Also, on the elbow/knee joints, the way you have it now would not deform properly. Check
this for limb deformations. Remake the tail, keep it straight this time. You can change it into a different pose later, but for now keep it straight so that the tail doesn't change its thickness at weird areas.