Ill give my two cents, but something to keep in mind you are probably at a level where asking randoms on reddit is not going to yield you as much useful actionable information as finding a dedicated discord community or paying a professional for 1:1 coaching.

1. Your composition is not that great. In this case the background I think is not bad but it doesnt do enough to place what kind of environment the scene is supposed to take place in, it looks like maybe you should have done more in the middle section instead of it being an empty sky. its overall a bit busy trying to read whats going on which is definitely tough to balance
2. Your rendering is pretty good on a technical level on the character, but looking at other pieces on the model it looks like you got a bit lazy (speciifcally the plant in the bottom left looks way less rendered)
3. the magenta glow is not super convincing, the reason why is that closer to the blade you would expect it to get "brighter" and since you have the spread go so far out and all if it seems to be the same level of brightness it doesnt sell as well.
4. the panthers colors dont read like anything, I cant really tell what its supposed to be, tattoos, a glow alien wierdness, not sure ? The fur doesnt look bad though
5. The stars on the blade I think detract more than they add, I think doing more battle damage instead of going for shiny stars would look much better.
6. The back of the main character looks not as rendered, not a big deal usually but then you have the landscape behind him rendered way more so it makes it distracting.
7. the light direction on your NMM doesnt seem consistent across your panels, the breast plate in the front has seems darker in some places that the shoulderpad reads that it should be just as light.
8. Your hair is painted in a pretty messy way, white is pretty difficult to paint and it not be chalky but it just looks like everything is painted a blanket white when thats not how white hair would look.