>>43642404I think some of them have trouble with the small details. The pixel-based limitation means that in order to communicate fine details you need to cheat and make them bigger. Look at the gyarados you just posted for example, the artist brought the head with all its little parts (eyes including iris and pupil, teeth, lips, crest, whiskers,...) forward, "closer to the camera" so to speak, such that those things are clearly visible. Meanwhile the less important, less detailed parts are placed further away. There's all sort of poses and perspective ideas one might use to achieve this, they need not be complicated but you can also do this to give a more active and dynamic look at the same time.
Meanwhile in the OP pic several of the mons are mostly parallel with the viewing plane. This would be fine if they didn't have details which are too small for this, eg. Thievul, whose facial features can just barely be made out. You can clearly see they just translated the official art as is, instead of adjusting the pose for pixel art. Obstagoon and a few others have similar issues.
On the other hand, you have Bolthund which is basically copied from the in-game 3D model pose and looks awful for this reason (boring "may-as-well-be-T-posed" pose, weird shading).
>>43642638agreed